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Turquoise is an
opaque Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shie ...
, blue-to-green
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
that is a
hydrous In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
of
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
and
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
, with the
chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...
. It is rare and valuable in finer grades and has been prized as a
gemstone A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...
for millennia due to its hue. The
robin egg blue Robin egg blue, also called eggshell blue or robin's-egg blue, is a shade of teal (a blue-green color), approximating the shade of the eggs laid by the American robin, an abundant songbird of North America. The egg pigment is biliverdin, a prod ...
or
sky blue Sky blue refers to a collection of shades comparable to that of a clear daytime sky. Typically it is a shade of cyan or light teal, though some iterations are closer to light Azure (color), azure or light blue. The term (as "sky blew") is atte ...
color of the
Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...
turquoise mined near the modern city of
Nishapur Nishapur or Neyshabur (, also ) is a city in the Central District (Nishapur County), Central District of Nishapur County, Razavi Khorasan province, Razavi Khorasan province, Iran, serving as capital of both the county and the district. Ni ...
,
Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
, has been used as a guiding reference for evaluating turquoise quality. Like most other opaque gems, turquoise has been devalued by the introduction of treatments, imitations, and synthetics into the market.


Names

The word ''turquoise'' dates to the 17th century and is derived from the
Old French Old French (, , ; ) was the language spoken in most of the northern half of France approximately between the late 8th [2-4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of French, that is, when it wa ...
''turquois'' meaning "Turkish" because the mineral was first brought to Europe through the Ottoman Empire.Turquoise
. minerals.usgs.gov
However, according to
Etymonline Etymonline, or ''Online Etymology Dictionary'', sometimes abbreviated as OED (not to be confused with the ''Oxford English Dictionary'', which the site often cites), is a free online dictionary that describes the etymology, origins of English la ...
, the word dates to the 14th century with the form ''turkeis'', meaning "Turkish", which was replaced with ''turqueise'' from French in the 1560s. According to the same source, the gemstone was first brought to Europe from
Turkestan Turkestan,; ; ; ; also spelled Turkistan, is a historical region in Central Asia corresponding to the regions of Transoxiana and East Turkestan (Xinjiang). The region is located in the northwest of modern day China and to the northwest of its ...
or another Turkic territory.
Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...
referred to the mineral as ''callais'' (from
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
) and the
Aztec The Aztecs ( ) were a Mesoamerican civilization that flourished in central Mexico in the Post-Classic stage, post-classic period from 1300 to 1521. The Aztec people included different Indigenous peoples of Mexico, ethnic groups of central ...
s knew it as ''chalchihuitl''. In professional mineralogy, until the mid-19th century, the scientific names ''kalaite''The Edinburgh Encyclopaedia, 1st American ed., Volume 13. — J. and E. Parker edition, 1832. or
azure spar Azure spar, sometimes azur-spar, is a trivial and commercial, partly obsolete name for several of the most famous bright blue or blue-colored minerals, which also have similar names, most notably for lazurite and azurite,''Krivovichev V. G.'' Mi ...
were also used, which simultaneously provided a version of the mineral origin of turquoise.Encyclopaedia Britannica, Volume fifth. — Edinburgh: printed for Archibald Constable and Company, 1824. However, these terms did not become widespread and gradually fell out of use.


History

Turquoise mining in New Mexico's Cerrillos Hills began with Native Americans, later attracting brief European interest in the late 1800s. Prices peaked in 1890, then collapsed by 1912, ending large-scale operations. During
Mohammad Khodabanda Mohammad Khodabanda (also spelled Khodabandeh; , born 1532; died 1595 or 1596) was the fourth Safavid dynasty, Safavid shah of Safavid Iran, Iran from 1578 until his overthrow in 1587 by his son Abbas I of Persia, Abbas I. Khodabanda had succeed ...
reign (1578-1587), accumulated turquoise dust from fifty years of mining in
Safavid Iran The Guarded Domains of Iran, commonly called Safavid Iran, Safavid Persia or the Safavid Empire, was one of the largest and longest-lasting Iranian empires. It was ruled from 1501 to 1736 by the Safavid dynasty. It is often considered the begi ...
was squandered lavishly, reflecting royal excess amid economic hardship, political discord, and rising factionalism among the qezelbash elite.


Properties

The finest of turquoise reaches a maximum
Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...
of just under 6, or slightly more than window
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
. Characteristically a
cryptocrystalline Cryptocrystalline is a rock microstructure, rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert a ...
mineral, turquoise almost never forms single
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s, and all of its properties are highly variable.
X-ray diffraction X-ray diffraction is a generic term for phenomena associated with changes in the direction of X-ray beams due to interactions with the electrons around atoms. It occurs due to elastic scattering, when there is no change in the energy of the waves. ...
testing shows its
crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices (an infinite array of discrete points). Space groups (symmetry groups ...
to be
triclinic class=skin-invert-image, 180px, Triclinic (a ≠ b ≠ c ≠ a and α, β, γ, 90° pairwise different) In crystallography, the triclinic (or anorthic) crystal system is one of the seven crystal systems. A crystal system is described by three b ...
. With lower hardness comes greater
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
. The lustre of turquoise is typically waxy to subvitreous, and its transparency is usually opaque, but may be semitranslucent in thin sections. Colour is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue and from a blue-green to a yellowish green. The blue is attributed to idiochromatic copper while the green may be the result of
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
impurities (replacing copper.) The
refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
of turquoise varies from 1.61 to 1.65 on the three crystal axes, with
birefringence Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...
0.040, biaxial positive, as measured from rare single crystals. Crushed turquoise is soluble in hot
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
. Its streak is white to greenish to blue, and its
fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
is smooth to
conchoidal A conchoidal fracture is a break or fracture of a brittle material that does not follow any natural planes of separation. Mindat.org defines ''conchoidal fracture'' as follows: "a fracture with smooth, curved surfaces, typically slightly concave, ...
. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of
pyrite The mineral pyrite ( ), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...
or interspersed with dark, spidery
limonite Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as , although this is not entirely accurate as the ratio of oxide to hydroxide can vary qu ...
veining. Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are rare. Typically the form is a vein or fracture filling, nodular, or
botryoidal A botryoidal ( ) texture or mineral habit, is one in which the mineral has an external form composed of many rounded segments, named for the Ancient Greek (), meaning "a bunch of grapes".Adjective form: ''botruoeidēs'' This is a common form f ...
in
habit A habit (or wont, as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously. A 1903 paper in the '' American Journal of Psychology'' defined a "habit, from the standpoint of psychology, ...
.
Stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...
forms have been reported. Turquoise may also
pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...
ously replace feldspar, apatite, other minerals, or even
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s. Odontolite is fossil bone or
ivory Ivory is a hard, white material from the tusks (traditionally from elephants) and Tooth, teeth of animals, that consists mainly of dentine, one of the physical structures of teeth and tusks. The chemical structure of the teeth and tusks of mamm ...
that has historically been thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate
vivianite Vivianite () is a hydrated iron(II) phosphate mineral found in a number of geological environments. Small amounts of manganese Mn2+, magnesium Mg2+, and calcium Ca2+ may substitute for iron Fe2+ in its structure.Gaines et al (1997) Dana's New ...
. Intergrowth with other secondary copper minerals such as
chrysocolla Chrysocolla ( ) is a hydrous copper phyllosilicate mineral and mineraloid with the formula (''x'' < 1) or . The structure of the mineral has been questioned, as a 2006 spectrographic study suggest ma ...
is also common. Turquoise is distinguished from chrysocolla, the only common mineral with similar properties, by its greater hardness. Turquoise forms a complete
solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...
series with chalcosiderite, , in which
ferric In chemistry, iron(III) or ''ferric'' refers to the chemical element, element iron in its +3 oxidation number, oxidation state. ''Ferric chloride'' is an alternative name for iron(III) chloride (). The adjective ''ferrous'' is used instead for i ...
iron replaces aluminium.


Formation

Turquoise deposits probably form in more than one way. However, a typical turquoise deposit begins with hydrothermal deposition of
copper sulfide Copper sulfides describe a family of chemical compounds and minerals with the formula CuxSy. Both minerals and synthetic materials comprise these compounds. Some copper sulfides are economically important ores. Prominent copper sulfide minerals ...
s. This takes place when hydrothermal fluids leach copper from a host rock, which is typically an
intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...
of
calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic ...
rock with a moderate to high
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
content that is relatively
oxidized Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
. The copper is redeposited in more concentrated form as a copper porphyry, in which veins of copper sulfide fill joints and fractures in the rock. Deposition takes place mostly in the potassic alteration zone, which is characterized by conversion of existing
feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...
to
potassium feldspar Potassium feldspar refers to a number of minerals in the feldspar group that contain large amounts of potassium in the crystal lattice. *Orthoclase (endmember formula K Al Si3 O8), an important tectosilicate mineral that forms igneous rock *Microcl ...
and deposition of
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...
s at a temperature of Turquoise is a secondary or
supergene A supergene is a chromosomal region encompassing multiple neighboring genes that are inherited together because of close genetic linkage, i.e. much less recombination than would normally be expected. This mode of inheritance can be due to genomic ...
mineral, not present in the original copper porphyry. It forms when
meteoric water Meteoric water, derived from precipitation such as snow and rain, includes water from lakes, rivers, and ice melts, all of which indirectly originate from precipitation. The journey of meteoric water from the atmosphere to the Earth's surface is a ...
(rain or snow melt infiltrating the
Earth's surface Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
) percolates through the copper porphyry. Dissolved oxygen in the water oxidizes the copper sulfides to soluble sulfates, and the acidic, copper-laden solution then reacts with aluminum and potassium minerals in the host rock to precipitate turquoise. This typically fills veins in volcanic rock or phosphate-rich sediments. Deposition usually takes place at a relatively low temperature, , and seems to occur more readily in arid environments. Turquoise in the
Sinai Peninsula The Sinai Peninsula, or simply Sinai ( ; ; ; ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a land bridge between Asia and Afri ...
is found in
lower Carboniferous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is sit ...
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
s overlain by
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
flows and
upper Carboniferous Upper may refer to: * Shoe upper or ''vamp'', the part of a shoe on the top of the foot * Stimulant, drugs which induce temporary improvements in either mental or physical function or both * ''Upper'', the original film title for the 2013 found f ...
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
. The overlying beds were presumably the source of the copper, which precipitated as turquoise in nodules, horizontal seams, or vertical joints in the sandstone beds. The classical Iranian deposits are found in sandstones and limestones of
Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...
age were intruded by
apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...
-rich
porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...
trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...
s and
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
rock. Supergene alteration fractured the rock and converted some of the minerals in the rock to
alunite Alunite is a hydroxylated aluminium potassium sulfate mineral, formula potassium, Kaluminium, Al3(sulfur, Soxygen, O4)2(Ohydrogen, H)6. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum ...
, which freed aluminum and phosphate to combine with copper from oxidized copper sulfides to form turquoise. This process took place at a relatively shallow depth, and by 1965 the mines had "bottomed" at a depth averaging just below the surface. Turquoise deposits are widespread in North America. Some deposits, such as those of Saguache and Conejos Counties in Colorado or the Cerrillos Hills in New Mexico, are typical supergene deposits formed from copper porphyries. The deposits in
Cochise County, Arizona Cochise County ( ) is a county in the southeastern corner of the U.S. state of Arizona. It is named after Cochise, a Chiricahua Apache who was a key war leader during the Apache Wars. The population was 125,447 at the 2020 census. The count ...
, are found in
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...
s and geologically young
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
s and go down at least as deep as .


Occurrence

Turquoise was among the first gems to be mined, and many historic sites have been depleted, though some are still worked to this day. These are all small-scale operations, often seasonal owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States. Deposits typically take the form of small
veins Veins () are blood vessels in the circulatory system of humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal c ...
in partially decomposed volcanic rock in arid climates.


Iran

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
has been an important source of turquoise for at least 2,000 years. It was initially named by Iranians "''pērōzah''" meaning "victory", and later the
Arabs Arabs (,  , ; , , ) are an ethnic group mainly inhabiting the Arab world in West Asia and North Africa. A significant Arab diaspora is present in various parts of the world. Arabs have been in the Fertile Crescent for thousands of yea ...
called it "''fayrūzah''", which is pronounced in Modern Persian as "''fīrūzeh''". In Iranian architecture, the blue turquoise was used to cover the
dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...
s of
palace A palace is a large residence, often serving as a royal residence or the home for a head of state or another high-ranking dignitary, such as a bishop or archbishop. The word is derived from the Latin name palātium, for Palatine Hill in Rome whi ...
s because its intense blue colour was also a symbol of heaven on earth. This deposit is blue naturally and turns green when heated due to dehydration. It is restricted to a mine-riddled region in
Nishapur Nishapur or Neyshabur (, also ) is a city in the Central District (Nishapur County), Central District of Nishapur County, Razavi Khorasan province, Razavi Khorasan province, Iran, serving as capital of both the county and the district. Ni ...
, the mountain peak of Ali-mersai near
Mashhad Mashhad ( ; ), historically also known as Mashad, Meshhed, or Meshed in English, is the List of Iranian cities by population, second-most-populous city in Iran, located in the relatively remote north-east of the country about from Tehran. ...
, the capital of
Khorasan Province Khorasan ( ; also transcribed as Khurasan, Xorasan and Khorassan), also called Traxiane during Hellenistic and Parthian Empire, Parthian times, was a Provinces of Iran, province in northeastern Iran until September 2004, when it was divided in ...
,
Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
. Weathered and broken
trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...
is host to the turquoise, which is found both ''in situ'' between layers of limonite and sandstone and amongst the
scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall. Landforms associated with these materials are often called talus deposits. The term ''scree'' is ap ...
at the mountain's base. These workings are the oldest known, together with those of the
Sinai Peninsula The Sinai Peninsula, or simply Sinai ( ; ; ; ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a land bridge between Asia and Afri ...
. Iran also has turquoise mines in Semnan and
Kerman Kerman (; ) is a city in the Central District (Kerman County), Central District of Kerman County, Kerman province, Kerman province, Iran, serving as capital of the province, the county, and the district. History Kerman was founded as a def ...
provinces.


Sinai

Since at least the First Dynasty (3000  BCE) in
ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
, and possibly before then, turquoise was used by the
Egyptians Egyptians (, ; , ; ) are an ethnic group native to the Nile, Nile Valley in Egypt. Egyptian identity is closely tied to Geography of Egypt, geography. The population is concentrated in the Nile Valley, a small strip of cultivable land stretchi ...
and was mined by them in the
Sinai Peninsula The Sinai Peninsula, or simply Sinai ( ; ; ; ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a land bridge between Asia and Afri ...
. This region was known as the ''Country of Turquoise'' by the native Monitu. There are six mines in the peninsula, all on its southwest coast, covering an area of some . The two most important of these mines, from a historical perspective, are
Serabit el-Khadim Serabit el-Khadim (Arabic language, Arabic: سرابيط الخادم Arabic pronunciation: Help:IPA/Arabic, araːˈbiːtˤ alˈxaːdɪm also transliterated Serabit al-Khadim, Serabit el-Khadem) is a locality in the southwest Sinai Peninsula, ...
and
Wadi Maghareh Wadi Maghareh (also spelled Maghara or Magharah, meaning "The Valley of Caves" in Egyptian Arabic) is an archaeological site located in the southwestern Sinai Peninsula, Egypt. It contains pharaonic monuments and turquoise mines dating from th ...
, believed to be among the oldest of known mines. The former mine is situated about 4 kilometres from an ancient temple dedicated to the deity
Hathor Hathor (, , , Meroitic language, Meroitic: ') was a major ancient Egyptian deities, goddess in ancient Egyptian religion who played a wide variety of roles. As a sky deity, she was the mother or consort of the sky god Horus and the sun god R ...
. The turquoise is found in
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
that is, or was originally, overlain by
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
. Copper and iron workings are present in the area. Large-scale turquoise mining is not profitable today, but the deposits are sporadically quarried by
Bedouin The Bedouin, Beduin, or Bedu ( ; , singular ) are pastorally nomadic Arab tribes who have historically inhabited the desert regions in the Arabian Peninsula, North Africa, the Levant, and Mesopotamia (Iraq). The Bedouin originated in the Sy ...
peoples using homemade
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, charcoal (which is mostly carbon), and potassium nitrate, potassium ni ...
. In the rainy winter months, miners face a risk from
flash flooding A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash flo ...
; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls may occur. The colour of Sinai material is typically greener than that of Iranian material but is thought to be stable and fairly durable. Often referred to as "Egyptian turquoise", Sinai material is typically the most translucent, and under magnification, its surface structure is revealed to be peppered with dark blue discs not seen in material from other localities.


United States

The
Southwest United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that includes Arizona and New Mexico, along with adjacent portions of California, Colorado, N ...
is a significant source of turquoise;
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
,
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
(
San Bernardino San Bernardino ( ) is a city in and the county seat of San Bernardino County, California, United States. Located in the Inland Empire region of Southern California, the city had a population of 222,101 in the 2020 census, making it the List of ...
, Imperial, Inyo counties),
Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
( Conejos,
El Paso El Paso (; ; or ) is a city in and the county seat of El Paso County, Texas, United States. The 2020 United States census, 2020 population of the city from the United States Census Bureau, U.S. Census Bureau was 678,815, making it the List of ...
,
Lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
, Saguache counties),
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
( Eddy, Grant, Otero, Santa Fe counties) and
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
(
Clark Clark is an English language surname with historical links to England, Scotland, and Ireland, ultimately derived from the Latin ''clericus'' meaning "scribe", "secretary" or a scholar within a religious order, referring to someone who was educated ...
, Elko, Esmeralda County,
Eureka Eureka often refers to: * Eureka (word), a famous exclamation attributed to Archimedes * Eureka effect, the sudden, unexpected realization of the solution to a problem Eureka or Ureka may also refer to: History * Eureka Rebellion, an 1854 g ...
, Lander, Mineral County and Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by
pre-Columbian In the history of the Americas, the pre-Columbian era, also known as the pre-contact era, or as the pre-Cabraline era specifically in Brazil, spans from the initial peopling of the Americas in the Upper Paleolithic to the onset of European col ...
Native Americans using stone tools, some local and some from as far away as central
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today. The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material is sometimes found, rivalling Iranian material in both colour and durability, most American turquoise is of a low grade (called "chalk turquoise"); high
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
levels mean greens and yellows predominate, and a typically friable consistency in the turquoise's untreated state precludes use in
jewelry Jewellery (or jewelry in American English) consists of decorative items worn for personal adornment such as brooches, ring (jewellery), rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be attached to the body or the ...
.
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
is currently the most important producer of turquoise by value. Several mines exist in the state, two of them famous for their unique colour and quality and considered the best in the industry: the Sleeping Beauty Mine in
Globe A globe is a spherical Earth, spherical Model#Physical model, model of Earth, of some other astronomical object, celestial body, or of the celestial sphere. Globes serve purposes similar to maps, but, unlike maps, they do not distort the surface ...
ceased turquoise mining in August 2012. The mine chose to send all ore to the crusher and to concentrate on copper production due to the rising price of copper on the world market. The price of natural untreated Sleeping Beauty turquoise has risen dramatically since the mine's closing. The Kingman Mine as of 2015 still operates alongside a copper mine outside of the city. Other mines include the Blue Bird mine, Castle Dome, and Ithaca Peak, but they are mostly inactive due to the high cost of operations and federal regulations. The
Phelps Dodge Phelps Dodge Corporation was an American mining company founded in 1834 as an import-export firm by Anson Greene Phelps and his two sons-in-law William Earle Dodge, Sr. and Daniel James. The latter two ran Phelps, James & Co., the part of the ...
Lavender Pit The Lavender Pit is a former open pit copper mine near Bisbee in Cochise County, Arizona, United States. It is located near the famous Copper Queen Mine. The Lavender Pit was named in honor of Harrison M. Lavender (1890–1952), who as Vice- ...
mine at Bisbee ceased operations in 1974 and never had a turquoise contractor. All Bisbee turquoise was "lunch pail" mined. It came out of the copper ore mine in miners' lunch pails. Morenci and Turquoise Peak are either inactive or depleted.
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
is the country's other major producer, with more than 120 mines which have yielded significant quantities of turquoise. Unlike elsewhere in the US, most Nevada mines have been worked primarily for their gem turquoise and very little has been recovered as a byproduct of other mining operations. Nevada turquoise is found as nuggets, fracture fillings and in
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
s as the cement filling interstices between fragments. Because of the geology of the Nevada deposits, a majority of the material produced is hard and dense, being of sufficient quality that no treatment or enhancement is required. While nearly every county in the state has yielded some turquoise, the chief producers are in Lander and Esmeralda counties. Most of the turquoise deposits in Nevada occur along a wide belt of
tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...
activity that coincides with the state's zone of
thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. I ...
ing. It strikes at a bearing of about 15° and extends from the northern part of Elko County, southward down to the California border southwest of Tonopah. Nevada has produced a wide diversity of colours and mixes of different matrix patterns, with turquoise from Nevada coming in various shades of blue, blue-green, and green. Some of this unusually-coloured turquoise may contain significant
zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
and
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
, which is the cause of the beautiful bright green to yellow-green shades. Some of the green to green-yellow shades may actually be
variscite Variscite is a hydrated aluminium phosphate mineral (). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color. The green color results from the presence of small amounts ...
or faustite, which are secondary phosphate minerals similar in appearance to turquoise. A significant portion of the Nevada material is also noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix". While a number of the Nevada deposits were first worked by Native Americans, the total
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
turquoise production since the 1870s has been estimated at more than , including nearly from the Carico Lake mine. In spite of increased costs, small scale mining operations continue at a number of turquoise properties in Nevada, including the Godber, Orvil Jack and Carico Lake mines in Lander County, the Pilot Mountain Mine in Mineral County, and several properties in the Royston and Candelaria areas of Esmerelda County. In 1912, the first deposit of distinct, single-crystal turquoise was discovered at Lynch Station in Campbell County,
Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...
. The crystals, forming a druse over the mother rock, are very small; is considered large. Until the 1980s Virginia was widely thought to be the only source of distinct crystals; there are now at least 27 other localities. In an attempt to recoup profits and meet demand, some American turquoise is treated or ''enhanced'' to a certain degree. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). There are some American mines which produce materials of high enough quality that no treatment or alterations are required. Any such treatments which have been performed should be disclosed to the buyer on sale of the material.


Other sources

Turquoise prehistoric artifacts (beads) are known since the fifth millennium BCE from sites in the
Eastern Rhodopes The Rhodopes (; , ; , ''Rodopi''; ) are a mountain range in Southeastern Europe, and the largest by area in Bulgaria, with over 83% of its area in the southern part of the country and the remainder in Greece. Golyam Perelik is its highest peak ...
in
Bulgaria Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...
– the source for the raw material is possibly related to the nearby Spahievo lead–zinc ore field. In Spain, turquoise has been found as a minor mineral in the variscite deposits exploited during prehistoric times in Palazuelos de las Cuevas (Zamora) and in Can Tintorer, Gavá (Barcelona).
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
has been a minor source of turquoise for 3,000 years or more. Gem-quality material, in the form of compact nodules, is found in the fractured, silicified
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
of Yunxian and Zhushan,
Hubei Hubei is a province of China, province in Central China. It has the List of Chinese provincial-level divisions by GDP, seventh-largest economy among Chinese provinces, the second-largest within Central China, and the third-largest among inland ...
province. Additionally,
Marco Polo Marco Polo (; ; ; 8 January 1324) was a Republic of Venice, Venetian merchant, explorer and writer who travelled through Asia along the Silk Road between 1271 and 1295. His travels are recorded in ''The Travels of Marco Polo'' (also known a ...
reported turquoise found in present-day
Sichuan Sichuan is a province in Southwestern China, occupying the Sichuan Basin and Tibetan Plateau—between the Jinsha River to the west, the Daba Mountains to the north, and the Yunnan–Guizhou Plateau to the south. Its capital city is Cheng ...
. Most Chinese material is exported, but a few carvings worked in a manner similar to
jade Jade is an umbrella term for two different types of decorative rocks used for jewelry or Ornament (art), ornaments. Jade is often referred to by either of two different silicate mineral names: nephrite (a silicate of calcium and magnesium in t ...
exist. In
Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...
, gem-quality deposits purportedly exist in the mountains of
Derge Derge (), officially Gengqing Town (; ), is a town in Dêgê County in Garzê Tibetan Autonomous Prefecture in Sichuan, China. It was once the center of the Kingdom of Derge in Kham. History Historically, Derge, which means "land of mercy", was ...
and Nagari-Khorsum in the east and west of the region respectively. Other notable localities include:
Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...
;
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
(
Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen of the United Kingdom and Empress of India * Victoria (state), a state of Australia * Victoria, British Columbia, Canada, a provincial capital * Victoria, Seychelles, the capi ...
and
Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
); north
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
; northern
Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
(
Chuquicamata Chuquicamata ( ; referred to as Chuqui for short) is the largest open-pit mining, open pit copper Mining, mine in terms of excavated volume in the world. It is located in the north of Chile, just outside Calama, Chile, Calama, at above sea level. ...
);
Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...
;
Saxony Saxony, officially the Free State of Saxony, is a landlocked state of Germany, bordering the states of Brandenburg, Saxony-Anhalt, Thuringia, and Bavaria, as well as the countries of Poland and the Czech Republic. Its capital is Dresden, and ...
;
Silesia Silesia (see names #Etymology, below) is a historical region of Central Europe that lies mostly within Poland, with small parts in the Czech Silesia, Czech Republic and Germany. Its area is approximately , and the population is estimated at 8, ...
; and
Turkestan Turkestan,; ; ; ; also spelled Turkistan, is a historical region in Central Asia corresponding to the regions of Transoxiana and East Turkestan (Xinjiang). The region is located in the northwest of modern day China and to the northwest of its ...
.


History of use

The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of
Ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
, the
Aztec The Aztecs ( ) were a Mesoamerican civilization that flourished in central Mexico in the Post-Classic stage, post-classic period from 1300 to 1521. The Aztec people included different Indigenous peoples of Mexico, ethnic groups of central ...
s (and possibly other Pre-Columbian
Mesoamerica Mesoamerica is a historical region and cultural area that begins in the southern part of North America and extends to the Pacific coast of Central America, thus comprising the lands of central and southern Mexico, all of Belize, Guatemala, El S ...
ns),
Persia Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
,
Mesopotamia Mesopotamia is a historical region of West Asia situated within the Tigris–Euphrates river system, in the northern part of the Fertile Crescent. Today, Mesopotamia is known as present-day Iraq and forms the eastern geographic boundary of ...
, the
Indus Valley The Indus ( ) is a transboundary river of Asia and a trans- Himalayan river of South and Central Asia. The river rises in mountain springs northeast of Mount Kailash in the Western Tibet region of China, flows northwest through the disp ...
, and to some extent in ancient
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
since at least the
Shang dynasty The Shang dynasty (), also known as the Yin dynasty (), was a Chinese royal dynasty that ruled in the Yellow River valley during the second millennium BC, traditionally succeeding the Xia dynasty and followed by the Western Zhou d ...
. Despite being one of the oldest gems, probably first introduced to
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
(through
Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
) with other
Silk Road The Silk Road was a network of Asian trade routes active from the second century BCE until the mid-15th century. Spanning over , it played a central role in facilitating economic, cultural, political, and religious interactions between the ...
novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the
Roman Catholic Church The Catholic Church (), also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.27 to 1.41 billion baptized Catholics Catholic Church by country, worldwid ...
's influence which allowed the use of turquoise in secular jewellery. It was apparently unknown in
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
until the
Mughal Mughal or Moghul may refer to: Related to the Mughal Empire * Mughal Empire of South Asia between the 16th and 19th centuries * Mughal dynasty * Mughal emperors * Mughal people, a social group of Central and South Asia * Mughal architecture * Mug ...
period, and unknown in
Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
until the 18th century. A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change colour with the wearer's health and protect him or her from untoward forces. The Aztecs viewed turquoise as an embodiment of fire and gave it properties such as heat and smokiness. They inlaid turquoise, together with
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
,
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
,
malachite Malachite () is a copper Carbonate mineral, carbonate hydroxide mineral, with the chemical formula, formula Basic copper carbonate, Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often for ...
, jet,
jade Jade is an umbrella term for two different types of decorative rocks used for jewelry or Ornament (art), ornaments. Jade is often referred to by either of two different silicate mineral names: nephrite (a silicate of calcium and magnesium in t ...
,
coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
, and shells, into provocative (and presumably ceremonial)
mosaic A mosaic () is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/Mortar (masonry), mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and ...
objects such as
mask A mask is an object normally worn on the face, typically for protection, disguise, performance, or entertainment, and often employed for rituals and rites. Masks have been used since antiquity for both ceremonial and practical purposes, ...
s (some with a
human skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominen ...
as their base),
knives A knife (: knives; from Old Norse 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced ...
, and
shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry like spears or long ranged projectiles suc ...
s. Natural
resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...
s,
bitumen Bitumen ( , ) is an immensely viscosity, viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American Engl ...
and
wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give lo ...
were used to bond the turquoise to the objects' base material; this was usually
wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...
, but
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
and shell were also used. Like the Aztecs, the
Pueblo Pueblo refers to the settlements of the Pueblo peoples, Native American tribes in the Southwestern United States, currently in New Mexico, Arizona, and Texas. The permanent communities, including some of the oldest continually occupied settlement ...
,
Navajo The Navajo or Diné are an Indigenous people of the Southwestern United States. Their traditional language is Diné bizaad, a Southern Athabascan language. The states with the largest Diné populations are Arizona (140,263) and New Mexico (1 ...
and
Apache The Apache ( ) are several Southern Athabaskan language-speaking peoples of the Southwestern United States, Southwest, the Southern Plains and Northern Mexico. They are linguistically related to the Navajo. They migrated from the Athabascan ho ...
tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the
archer Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In modern ...
dead aim. In Navajo culture it is used for "a spiritual protection and blessing." Among these peoples turquoise was used in
mosaic A mosaic () is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/Mortar (masonry), mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and ...
inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants. The
Ancestral Puebloans The Ancestral Puebloans, also known as Ancestral Pueblo peoples or the Basketmaker-Pueblo culture, were an ancient Native American culture of Pueblo peoples spanning the present-day Four Corners region of the United States, comprising southe ...
(Anasazi) of the
Chaco Canyon Chaco Culture National Historical Park is a United States National Historical Park in the American Southwest hosting a large concentration of pre-Columbian indigenous ruins of pueblos. The park is located in northwestern New Mexico, betwee ...
and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects. The distinctive
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
jewellery produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from around 1880 as a result of European influences. In Persia, turquoise was the ''de facto'' national stone for millennia, extensively used to decorate objects (from
turban A turban (from Persian language, Persian دولبند‌, ''dolband''; via Middle French ''turbant'') is a type of headwear based on cloth winding. Featuring many variations, it is worn as customary headwear by people of various cultures. Commun ...
s to
bridle A bridle is a piece of equipment used to direct a horse. As defined in the ''Oxford English Dictionary'', the "bridle" includes both the that holds a bit that goes in the mouth of a horse, and the reins that are attached to the bit. It prov ...
s),
mosque A mosque ( ), also called a masjid ( ), is a place of worship for Muslims. The term usually refers to a covered building, but can be any place where Salah, Islamic prayers are performed; such as an outdoor courtyard. Originally, mosques were si ...
s, and other important buildings both inside and out, such as the Medresseh-i Shah Husein Mosque of
Isfahan Isfahan or Esfahan ( ) is a city in the Central District (Isfahan County), Central District of Isfahan County, Isfahan province, Iran. It is the capital of the province, the county, and the district. It is located south of Tehran. The city ...
. The Persian style and use of turquoise was later brought to
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
following the establishment of the Mughal Empire there, its influence seen in high purity
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
jewellery (together with
ruby Ruby is a pinkish-red-to-blood-red-colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapph ...
and
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...
) and in such buildings as the
Taj Mahal The Taj Mahal ( ; ; ) is an ivory-white marble mausoleum on the right bank of the river Yamuna in Agra, Uttar Pradesh, India. It was commissioned in 1631 by the fifth Mughal Empire, Mughal emperor, Shah Jahan () to house the tomb of his belo ...
. Persian turquoise was often
engraved Engraving is the practice of incising a design on a hard, usually flat surface by cutting grooves into it with a burin. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an inta ...
with devotional words in
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
script which was then inlaid with gold.
Cabochon A cabochon (; ) is a gemstone that has been shaped and polished, as opposed to faceted. The resulting form is usually a convex (rounded) obverse with a flat reverse. Cabochon was the default method of preparing gemstones before gemstone cuttin ...
s of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold jewellery of
Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...
and
Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...
, where a greener hue is said to be preferred. Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style. The
Ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
ian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from
Tutankhamun Tutankhamun or Tutankhamen, (; ), was an Egyptian pharaoh who ruled during the late Eighteenth Dynasty of Egypt, Eighteenth Dynasty of ancient Egypt. Born Tutankhaten, he instituted the restoration of the traditional polytheistic form of an ...
's tomb, most notably the
Pharaoh Pharaoh (, ; Egyptian language, Egyptian: ''wikt:pr ꜥꜣ, pr ꜥꜣ''; Meroitic language, Meroitic: 𐦲𐦤𐦧, ; Biblical Hebrew: ''Parʿō'') was the title of the monarch of ancient Egypt from the First Dynasty of Egypt, First Dynasty ( ...
's iconic burial mask which was liberally inlaid with the stone. It also adorned rings and great sweeping
necklace A necklace is an article of jewellery that is worn around the neck. Necklaces may have been one of the earliest types of adornment worn by humans. They often serve ceremonial, religious, magical, or funerary purposes and are also used as sy ...
s called '' pectorals''. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by
carnelian Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used int ...
,
lapis lazuli Lapis lazuli (; ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color. Originating from the Persian word for the gem, ''lāžward'', lapis lazuli is ...
, and in later pieces, coloured
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
. Turquoise, associated with the goddess
Hathor Hathor (, , , Meroitic language, Meroitic: ') was a major ancient Egyptian deities, goddess in ancient Egyptian religion who played a wide variety of roles. As a sky deity, she was the mother or consort of the sky god Horus and the sun god R ...
, was so liked by the Ancient Egyptians that it became (arguably) the first gemstone to be imitated, the fair structure created by an artificial glazed
ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
product known as
faience Faience or faïence (; ) is the general English language term for fine tin-glazed pottery. The invention of a white Ceramic glaze, pottery glaze suitable for painted decoration, by the addition of an stannous oxide, oxide of tin to the Slip (c ...
. The French conducted
archaeological Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of Artifact (archaeology), artifacts, architecture, biofact (archaeology), biofacts or ecofacts, ...
excavations of Egypt from the mid-19th century through the early 20th. These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing jewellery,
architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...
, and
art Art is a diverse range of cultural activity centered around ''works'' utilizing creative or imaginative talents, which are expected to evoke a worthwhile experience, generally through an expression of emotional power, conceptual ideas, tec ...
of the time. Turquoise, already favoured for its pastel shades since around 1810, was a staple of
Egyptian Revival Egyptian Revival is an architectural style that uses the motifs and imagery of ancient Egypt. It is attributed generally to the public awareness of ancient Egyptian monuments generated by Napoleon's French campaign in Egypt and Syria, invasion of ...
pieces. In contemporary Western use, turquoise is most often encountered cut '' en cabochon'' in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. Lesser material may be carved into
fetishes A fetish is an object believed to have supernatural powers, or in particular, a human-made object that has power over others. Essentially, fetishism is the attribution of inherent non-material value, or powers, to an object. Talismans and amulets ...
, such as those crafted by the Zuni. While strong sky blues remain superior in value, mottled green and yellowish material is popular with
artisan An artisan (from , ) is a skilled craft worker who makes or creates material objects partly or entirely by hand. These objects may be functional or strictly decorative, for example furniture, decorative art, sculpture, clothing, food ite ...
s.


Cultural associations

The goddess
Hathor Hathor (, , , Meroitic language, Meroitic: ') was a major ancient Egyptian deities, goddess in ancient Egyptian religion who played a wide variety of roles. As a sky deity, she was the mother or consort of the sky god Horus and the sun god R ...
was associated with turquoise, as she was the patroness of
Serabit el-Khadim Serabit el-Khadim (Arabic language, Arabic: سرابيط الخادم Arabic pronunciation: Help:IPA/Arabic, araːˈbiːtˤ alˈxaːdɪm also transliterated Serabit al-Khadim, Serabit el-Khadem) is a locality in the southwest Sinai Peninsula, ...
, where it was mined. Her titles included "Lady of Turquoise", "Mistress of Turquoise", and "Lady of Turquoise Country". In Western culture, turquoise is also the traditional
birthstone A birthstone is a gemstone that represents a person's birth period, usually the month or zodiac sign. Birthstones are often worn as jewelry or a pendant necklace. History of birthstones Western custom The first-century historian Josephus bel ...
for those born in the month of December. The turquoise is also a stone in the Jewish
High Priest The term "high priest" usually refers either to an individual who holds the office of ruler-priest, or to one who is the head of a religious organisation. Ancient Egypt In ancient Egypt, a high priest was the chief priest of any of the many god ...
's
breastplate A breastplate or chestplate is a device worn over the torso to protect it from injury, as an item of religious significance, or as an item of status. European In medieval weaponry, the breastplate is the front portion of plate armour covering th ...
, described in
Exodus Exodus or the Exodus may refer to: Religion * Book of Exodus, second book of the Hebrew Torah and the Christian Bible * The Exodus, the biblical story of the migration of the ancient Israelites from Egypt into Canaan Historical events * Ex ...
chapter 28. The stone is also considered sacred to the indigenous Zuni and
Pueblo Pueblo refers to the settlements of the Pueblo peoples, Native American tribes in the Southwestern United States, currently in New Mexico, Arizona, and Texas. The permanent communities, including some of the oldest continually occupied settlement ...
peoples of the American Southwest. The pre-Columbian
Aztec The Aztecs ( ) were a Mesoamerican civilization that flourished in central Mexico in the Post-Classic stage, post-classic period from 1300 to 1521. The Aztec people included different Indigenous peoples of Mexico, ethnic groups of central ...
and
Maya Maya may refer to: Ethnic groups * Maya peoples, of southern Mexico and northern Central America ** Maya civilization, the historical civilization of the Maya peoples ** Mayan languages, the languages of the Maya peoples * Maya (East Africa), a p ...
also considered it to be a valuable and culturally important stone.


Imitations

The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product
faience Faience or faïence (; ) is the general English language term for fine tin-glazed pottery. The invention of a white Ceramic glaze, pottery glaze suitable for painted decoration, by the addition of an stannous oxide, oxide of tin to the Slip (c ...
. Later glass and enamel were also used, and in modern times more sophisticated
porcelain Porcelain (), also called china, is a ceramic material made by heating Industrial mineral, raw materials, generally including kaolinite, in a kiln to temperatures between . The greater strength and translucence of porcelain, relative to oth ...
,
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
s, and various assembled, pressed, bonded, and
sintered Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, pla ...
products (composed of various copper and aluminium compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated
aluminium phosphate Aluminium phosphate is a chemical compound. In nature it occurs as the mineral berlinite. Many synthetic forms of aluminium phosphate are known. They have framework structures similar to zeolites and some are used as catalysts, ion-exchangers o ...
coloured by copper oleate; and "neolith", a mixture of
bayerite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3). It is also sometimes called hydrargillite (or hydrargyllite). Gibbsite is an important ore of aluminium ...
and copper(II) phosphate. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 Pierre Gilson introduced one fairly close to a true
synthetic Synthetic may refer to: Science * Synthetic biology * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic elements, chemical elements that are not naturally found on Earth and therefore have to be created in ...
(it does differ in chemical composition owing to a binder used, meaning it is best described as a simulant rather than a synthetic). Gilson turquoise is made in both a uniform colour and with black "spiderweb matrix" veining not unlike the natural Nevada material. The most common imitation of turquoise encountered today is dyed
howlite Howlite, a calcium borosilicate hydroxide ( Ca2 B5 Si O9(O H)5), is a borate mineral found in evaporite deposits.
and
magnesite Magnesite is a mineral with the chemical formula ( magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts. Occurrence Magnesite occurs as veins in and an alteration product of ultramafic r ...
, both white in their natural states, and the former also having natural (and convincing) black veining similar to that of turquoise. Dyed
chalcedony Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic ...
,
jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to ...
, and
marble Marble is a metamorphic rock consisting of carbonate minerals (most commonly calcite (CaCO3) or Dolomite (mineral), dolomite (CaMg(CO3)2) that have recrystallized under the influence of heat and pressure. It has a crystalline texture, and is ty ...
is less common, and much less convincing. Other natural materials occasionally confused with or used in lieu of turquoise include:
variscite Variscite is a hydrated aluminium phosphate mineral (). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color. The green color results from the presence of small amounts ...
and faustite;
chrysocolla Chrysocolla ( ) is a hydrous copper phyllosilicate mineral and mineraloid with the formula (''x'' < 1) or . The structure of the mineral has been questioned, as a 2006 spectrographic study suggest ma ...
(especially when impregnating
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
);
lazulite Lazulite or ''Azure spar'Krivovichev V. G.'' Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. ''(in Russian)'' is a transparent to semi-opaque, blue mineral that is ...
;
smithsonite Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate ( Zn CO3). Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in a ...
;
hemimorphite Hemimorphite is the chemical compound Zinc, Zn4(Pyrosilicate, Si2O7)(Hydroxide, OH)2Water of crystallization, ·H2O, a component of mineral Calamine (mineral), calamine. It is a silicate mineral which, together with smithsonite (ZnCO3), has bee ...
;
wardite Wardite is a hydrous sodium aluminium phosphate hydroxide mineral with formula: Na Al3( P O4)2(O H)4·2( H2O). Wardite is of interest for its rare crystallography. It crystallizes in the tetragonal trapezohedral class and is one of only a few ...
; and a
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
bone or
tooth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...
called odontolite or "bone turquoise", coloured blue naturally by the mineral
vivianite Vivianite () is a hydrated iron(II) phosphate mineral found in a number of geological environments. Small amounts of manganese Mn2+, magnesium Mg2+, and calcium Ca2+ may substitute for iron Fe2+ in its structure.Gaines et al (1997) Dana's New ...
. While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern
France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
. These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour (usually a uniform dark blue) and texture (usually granular or sugary). Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. Staining between grain boundaries may be visible in dyed imitations. Some destructive tests may be necessary; for example, the application of diluted
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
will cause the
carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
s odontolite and magnesite to
effervesce Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb ''fervere'' (to boil), preceded by the adverb ''ex''. It has the same l ...
and howlite to turn green, while a heated probe may give rise to the pungent smell so indicative of plastic. Differences in
specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...
,
refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
, light absorption (as evident in a material's
absorption spectrum Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, ...
), and other physical and optical properties are also considered as means of separation.


Treatments

Turquoise is treated to enhance both its colour and durability (increased
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...
and decreased
porosity Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
). As is so often the case with any precious stones, full disclosure about treatment is frequently not given. Gemologists can detect these treatments using a variety of testing methods, some of which are destructive, such as the use of a heated probe applied to an inconspicuous spot, which will reveal oil, wax or plastic treatment.


Waxing and oiling

Historically, light waxing and oiling were the first treatments used in ancient times, providing a wetting effect, thereby enhancing the colour and lustre. This treatment is more or less acceptable by tradition, especially because treated turquoise is usually of a higher grade to begin with. Oiled and waxed stones are prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. (With some skill, oil and wax treatments can be restored.)


Backing

Since finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material for reinforcement. These stones are termed "backed", and it is standard practice that all thinly cut turquoise in the Southwestern United States is backed. Native indigenous peoples of this region, because of their considerable use and wearing of turquoise, have found that backing increases the durability of thinly cut slabs and cabochons of turquoise. They observe that if the stone is not backed it will often crack. Backing of turquoise is not widely known outside of the Native American and Southwestern United States jewellery trade. Backing does not diminish the value of high quality turquoise, and indeed the process is expected for most thinly cut American commercial gemstones.


Zachery treatment

A proprietary process was created by electrical engineer and turquoise dealer James E. Zachery in the 1980s to improve the stability of medium to high-grade turquoise. The process can be applied in several ways: either through deep penetration on rough turquoise to decrease porosity, by shallow treatment of finished turquoise to enhance color, or both. The treatment can enhance color and improve the turquoise's ability to take a polish. Such treated turquoise can be distinguished in some cases from natural turquoise, without destruction, by
energy-dispersive X-ray spectroscopy Energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS or XEDS), sometimes called energy dispersive X-ray analysis (EDXA or EDAX) or energy dispersive X-ray microanalysis (EDXMA), is an analytical technique used for the elemental analysis or chemi ...
, which can detect its elevated potassium levels. In some instances, such as with already high-quality, low-porosity turquoise that is treated only for porosity, the treatment is undetectable.


Dyeing

The use of
Prussian blue Prussian blue (also known as Berlin blue, Brandenburg blue, Parisian and Paris blue) is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula . It consists of cations, where iron is in the oxidat ...
and other dyes (often in conjunction with bonding treatments) to "enhance” its appearance, make uniform or completely change the colour, is regarded as fraudulent by some purists, especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise.


Stabilization

Material treated with plastic or water glass is termed "bonded" or "stabilized" turquoise. This process consists of pressure impregnation of otherwise unsaleable chalky American material by
epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...
and
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
s (such as
polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It i ...
) and water glass (sodium silicate) to produce a wetting effect and improve durability. Plastic and water glass treatments are far more permanent and stable than waxing and oiling, and can be applied to material too chemically or physically unstable for oil or wax to provide sufficient improvement. Conversely, stabilization and bonding are rejected by some as too radical an alteration. The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today.


Reconstitution

Perhaps the most extreme of treatments is "reconstitution", wherein fragments of fine turquoise material, too small to be used individually, are powdered and then bonded with resin to form a solid mass. Very often the material sold as "reconstituted turquoise" is
artificial Artificiality (the state of being artificial, anthropogenic, or man-made) is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity. Connotati ...
, with little or no natural stone, made entirely from resins and dyes. In the trade reconstituted turquoise is often called "block turquoise" or simply "block".


Valuation and care

Hardness and richness of colour are two of the major factors in determining the value of turquoise; while colour is a matter of individual taste, generally speaking, the most desirable is a strong
sky The sky is an unobstructed view upward from the planetary surface, surface of the Earth. It includes the atmosphere of Earth, atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from ...
to
robin egg blue Robin egg blue, also called eggshell blue or robin's-egg blue, is a shade of teal (a blue-green color), approximating the shade of the eggs laid by the American robin, an abundant songbird of North America. The egg pigment is biliverdin, a prod ...
(in reference to the eggs of the
American robin The American robin (''Turdus migratorius'') is a migratory bird of the true thrush genus and Turdidae, the wider thrush family. It is named after the European robin because of its reddish-orange breast, though the two species are not clos ...
). Whatever the colour, for many applications, turquoise should not be soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolour over time and will not hold up to normal use in jewellery. The mother rock or ''matrix'' in which turquoise is found can often be seen as splotches or a network of brown or black veins running through the stone in a netted pattern; this veining may add value to the stone if the result is complementary, but such a result is uncommon. Such material is sometimes described as "spiderweb matrix"; it is most valued in the
Southwest United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that includes Arizona and New Mexico, along with adjacent portions of California, Colorado, N ...
and
Far East The Far East is the geographical region that encompasses the easternmost portion of the Asian continent, including North Asia, North, East Asia, East and Southeast Asia. South Asia is sometimes also included in the definition of the term. In mod ...
, but is not highly appreciated in the
Near East The Near East () is a transcontinental region around the Eastern Mediterranean encompassing the historical Fertile Crescent, the Levant, Anatolia, Egypt, Mesopotamia, and coastal areas of the Arabian Peninsula. The term was invented in the 20th ...
where unblemished and vein-free material is ideal (regardless of how complementary the veining may be). Uniformity of colour is desired, and in finished pieces the quality of workmanship is also a factor; this includes the quality of the polish and the symmetry of the stone. Calibrated stones—that is, stones adhering to standard jewellery setting measurements—may also be more sought after. Like
coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimetres rather than weight. Turquoise is treated in many different ways, some more permanent and radical than others. Controversy exists as to whether some of these treatments should be acceptable, but one can be more or less forgiven universally: This is the ''light''
wax Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give lo ...
ing or
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
ing applied to most gem turquoise to improve its colour and lustre; if the material is of high quality to begin with, very little of the wax or oil is absorbed and the turquoise therefore does not rely on this impermanent treatment for its beauty. All other factors being equal, untreated turquoise will always command a higher price. Bonded and reconstituted material is worth considerably less. Being a
phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
mineral, turquoise is inherently fragile and sensitive to solvents;
perfume Perfume (, ) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agre ...
and other
cosmetics Cosmetics are substances that are intended for application to the body for cleansing, beautifying, promoting attractiveness, or altering appearance. They are mixtures of chemical compounds derived from either Natural product, natural source ...
will attack the finish and may alter the colour of turquoise gems, as will skin oils, as will most commercial jewellery cleaning fluids. Prolonged exposure to direct sunlight may also discolour or dehydrate turquoise. Care should therefore be taken when wearing such jewels: cosmetics, including
sunscreen Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...
and
hair spray Hair spray (also hair lacquer or spritz) is a common cosmetic hairstyling product that is sprayed onto hair to protect against humidity and wind and have it stay in a desired shape. Hair sprays typically consist of several components for the ...
, should be applied before putting on turquoise jewellery, and they should not be worn to a beach or other sun-bathed environment. After use, turquoise should be gently cleaned with a soft cloth to avoid a buildup of residue, and should be stored in its own container to avoid scratching by harder gems. Turquoise can also be adversely affected if stored in an airtight container.


See also

* , with a deep blue color * , with a deep blue color * , with a deep blue color *
List of minerals This is a list of minerals which have Wikipedia articles. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various ''species''. Within a mineral speci ...
* of pale green color due to trivalent chromium ()


References


Further reading

* * * * * *


External links

* {{Authority control Aluminium minerals Copper(II) minerals Gemstones Phosphate minerals Symbols of New Mexico Triclinic minerals Symbols of Arizona Tetrahydrate minerals Minerals in space group 2