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Jet is a type of
lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
, the lowest
rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as: Level or position in a hierarchical organization * Academic rank * Diplomatic rank * Hierarchy * ...
of
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
, and is a
gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
. Unlike many gemstones, jet is not a
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
, but is rather a
mineraloid A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an a ...
. It is derived from wood that has changed under extreme pressure. The English noun ''jet'' derives from the French word for the same material, (modern French ), ultimately referring to the ancient town of Gagae. Jet is either black or dark brown, but may contain
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
inclusions which are of brassy colour and metallic lustre. The adjective " jet-black", meaning as dark a black as possible, derives from this material.


Origin

Jet is a product of decomposition of wood from millions of years ago, commonly the wood of trees of the family Araucariaceae. Jet is found in two forms, hard and soft. Hard jet is the result of carbon compression and salt water; soft jet may be the result of carbon compression and fresh water. Despite the name they both occupy the same area of the Mohs scale with the difference being that soft jet is more likely to crack when exposed to changes in temperature.


Properties

Jet is around 75% carbon and 12% oxygen with sulfur and hydrogen making up most of the balance. Other elements are found at trace level and the exact ratios varying with the source; for example, Spanish jet contains more sulfur than Whitby jet. Jet has a Mohs
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
ranging between 2.5 and 4 and a
specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its dens ...
of 1.30 to 1.34. The
refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, ...
of jet is approximately 1.66. The touch of a red-hot needle should cause jet to emit an odour similar to coal. Jet may induce an
electric charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons res ...
like that of amber when rubbed. Jet is very easy to carve, but it is difficult to create fine details without breaking so it takes an experienced lapidarist to execute more elaborate carvings.


Location


England

The jet found at
Whitby Whitby is a seaside town, port and civil parish in the Scarborough borough of North Yorkshire, England. Situated on the east coast of Yorkshire at the mouth of the River Esk, Whitby has a maritime, mineral and tourist heritage. Its East Cl ...
, in England, is the "''Jet Rock''" unit of the Mulgrave Shale Member, which is part of the Whitby Mudstone Formation. This jet deposit was formed approximately 181 million years ago, during the
Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toar ...
age of the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
epoch. Whitby Jet is the fossilized wood from species similar to the extant Chilean pine ('' Araucaria araucana'').Oliver, N., 2012, ''A History of Ancient Britain'', Phoenix Paperback, The deposit extends throughout
North York Moors National Park North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north' ...
. Jet has also been found in Kimmeridge shale seams in Dorset.


France

Jet was mined from a number of areas of France including Montjardin and Roquevaire. Raw jet was also imported from Spain. In the 18th century there was a jet working industry based around Sainte-Colombe-sur-l'Hers and La Bastide-sur-l'Hers but this declined with the start of the 19th. An 1871 plan to import raw French jet into Whitby was unsuccessful due to its poor quality.


Spain

The jet found in
Asturias Asturias (, ; ast, Asturies ), officially the Principality of Asturias ( es, Principado de Asturias; ast, Principáu d'Asturies; Galician-Asturian: ''Principao d'Asturias''), is an autonomous community in northwest Spain. It is coextensiv ...
, the biggest deposit in northern Spain, is of Late Jurassic ( Kimmeridgian) age, about 155 million years old. Asturian jet is a perhydrous coal that suffered an anomalous coalification process and presents great material stability over long periods of time. Jet is also found near
Santiago de Compostela Santiago de Compostela is the capital of the autonomous community of Galicia, in northwestern Spain. The city has its origin in the shrine of Saint James the Great, now the Cathedral of Santiago de Compostela, as the destination of the Way of S ...
in northwest Spain


United States

Native American
Navajo The Navajo (; British English: Navaho; nv, Diné or ') are a Native Americans in the United States, Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest fe ...
and
Pueblo In the Southwestern United States, Pueblo (capitalized) refers to the Native tribes of Puebloans having fixed-location communities with permanent buildings which also are called pueblos (lowercased). The Spanish explorers of northern New Spain ...
tribes of
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...
were using regionally mined jet for jewellery and the ornamentation of weapons when early Spanish explorers reached the area in the 1500s. Today these jet deposits are known as Acoma jet, for the Acoma Pueblo. Enormous coal deposits characterize the San Juan Basin of New Mexico and this geology is closely related to jet deposits mined in the Henry Mountains of
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...
and the
Front Range The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encountered ...
of El Paso County,
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...
.


Other locations

Jet is also commercialized in Poland and near
Erzurum Erzurum (; ) is a city in eastern Anatolia, Turkey. It is the largest city and capital of Erzurum Province and is 1,900 meters (6,233 feet) above sea level. Erzurum had a population of 367,250 in 2010. The city uses the double-headed eagle as ...
in Turkey, where it is known as
oltu stone Oltu stone ( tr, Oltu taşı) is a kind of jet found in the region around Oltu town within Erzurum Province, eastern Turkey. The organic substance is used as semi-precious gemstone in manufacturing jewellery. Location and extraction Oltu stone, ...
and is used to make
prayer beads Prayer beads are a form of beadwork used to count the repetitions of prayers, chants, or mantras by members of various religions such as Hinduism, Buddhism, Shinto, Umbanda, Islam, Sikhism, the Baháʼí Faith, and some Christian denom ...
.


History

The earliest known worked jet object is a 10,000 BC model of a botfly larva, from Baden-Württemberg, Germany, found among the Venuses of Petersfels. Jet has been used in Britain since the
Neolithic period The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several parts ...
It continued in use in Britain through the
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
where it was used for necklace beads. Jet necklaces following the plate and spacer design may have been based on Gold lunula. During the
Iron Age The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age ( Paleolithic, Mesolithic, Neolithic) and the Bronze Age ( Chalcolithic). The concept has been mostly ...
jet went out of fashion until the early 3rd century AD in
Roman Britain Roman Britain was the period in classical antiquity when large parts of the island of Great Britain were under occupation by the Roman Empire. The occupation lasted from AD 43 to AD 410. During that time, the territory conquered wa ...
. The end of Roman Britain marked the end of jet's ancient popularity. Early archaeologists (particularly Victorian) often failed to distinguish between jet and other jet-like materials In particular in southern Britain the material described as jet was often Kimmeridge Shale. and some artifacts use more than one jet-like material. For example the Pen y Bonc necklace combines two or three jet pieces with other dark material.


Roman use

Whitby jet was a popular material for jewellery in Roman Britain from the 3rd century onward.There is no evidence for Roman jet working in
Whitby Whitby is a seaside town, port and civil parish in the Scarborough borough of North Yorkshire, England. Situated on the east coast of Yorkshire at the mouth of the River Esk, Whitby has a maritime, mineral and tourist heritage. Its East Cl ...
itself, rather it was transferred to
Eboracum Eboracum () was a fort and later a city in the Roman province of Britannia. In its prime it was the largest town in northern Britain and a provincial capital. The site remained occupied after the decline of the Western Roman Empire and ultimat ...
(modern
York York is a cathedral city with Roman origins, sited at the confluence of the rivers Ouse and Foss in North Yorkshire, England. It is the historic county town of Yorkshire. The city has many historic buildings and other structures, such as a ...
) where considerable evidence for jet production has been found.Ottaway, P., 2004, ''Roman York'', Tempus: Stroud The collection of jet at this time was based on
beachcombing Beachcombing is an activity that consists of an individual "combing" (or searching) the beach and the intertidal zone, looking for things of value, interest or utility. A beachcomber is a person who participates in the activity of beachcombing. ...
rather than quarrying. It was used in rings, hair pins, beads, bracelets, bangles, necklaces, and pendants, many of which are visible in the
Yorkshire Museum The Yorkshire Museum is a museum in York, England. It was opened in 1830, and has five permanent collections, covering biology, geology, archaeology, numismatics and astronomy. History The museum was founded by the Yorkshire Philosophical Soc ...
. Jet rings tended to follow the styles of existing metal rings although there were exceptions. Jet pendants were carved cameo style with
Medusa In Greek mythology, Medusa (; Ancient Greek: Μέδουσα "guardian, protectress"), also called Gorgo, was one of the three monstrous Gorgons, generally described as winged human females with living venomous snakes in place of hair. Those ...
head being a popular theme. Stylistic similarities with jet items found in the Rhineland, and lack of any evidence for local manufacture, suggest that
Eboracum Eboracum () was a fort and later a city in the Roman province of Britannia. In its prime it was the largest town in northern Britain and a provincial capital. The site remained occupied after the decline of the Western Roman Empire and ultimat ...
-produced items were exported to that area. One item that has been found around the Rhine but not in Britain are jet bracelets that feature grooves with gold inserts. In the Roman period it saw use as a magical material, frequently used in amulets and pendants because of its supposed protective qualities and ability to deflect the gaze of the
evil eye The Evil Eye ( grc, ὀφθαλμὸς βάσκανος; grc-koi, ὀφθαλμὸς πονηρός; el, (κακό) μάτι; he, עַיִן הָרָע, ; Romanian: ''Deochi''; it, malocchio; es, mal de ojo; pt, mau-olhado, olho gordo; ar ...
.
Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...
suggests that "the kindling of jet drives off snakes and relieves suffocation of the uterus. Its fumes detect attempts to simulate a disabling illness or a state of virginity." It has been referenced by other ancient writers including
Solinus Solinus may refer to: * Gaius Julius Solinus, a 3rd century Latin author * Solinus (horse), a British racehorse (1975–1979) * Solinus, Duke of Ephesus, a character in William Shakespeare's play ''The Comedy of Errors'' See also * Salinas (disam ...
and
Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be o ...
.


Viking use

Vikings made some use of jet including rings and miniature sculptures of animals with snakes being a prominent theme. The source of the jet hasn't been confirmed although Whitby is the most likely possibility.


Medieval

Medieval jet use appears to have been largely limited to religious items such as crosses and
Rosary The Rosary (; la, , in the sense of "crown of roses" or "garland of roses"), also known as the Dominican Rosary, or simply the Rosary, refers to a set of prayers used primarily in the Catholic Church, and to the physical string of knots or ...
beads. During the period there was a belief that water drunk from jet bowls could help with labour. A jet bowl held in the
Museum of London The Museum of London is a museum in London, covering the history of the UK's capital city from prehistoric to modern times. It was formed in 1976 by amalgamating collections previously held by the City Corporation at the Guildhall Museum (fou ...
may have been designed to allow for this.


Victorian use

Jet as a gemstone became fashionable during the reign of
Queen Victoria Victoria (Alexandrina Victoria; 24 May 1819 – 22 January 1901) was Queen of the United Kingdom of Great Britain and Ireland from 20 June 1837 until her death in 1901. Her reign of 63 years and 216 days was longer than that of any previ ...
. It originally became fashionable in the 1850s after the queen wore a necklace of it as part of mourning dress for
Princess Victoria of Saxe-Coburg and Gotha Princess Victoria of Saxe-Coburg and Gotha (Victoria Franziska Antonia Juliane Luise, Victoire Francoise Antoinette Julianne Louise); 14 February 1822 – 10 November 1857) was the daughter of Ferdinand, Prince of Saxe-Coburg and Gotha-Kohá ...
. Later the Queen wore Whitby jet as part of her mourning dress while mourning the death of Prince Albert. In some jewellery designs of the period jet was combined with cut steel. Jet use was at its highest in the early 1870s and from there it declined. From above 1000 workers in the trade Whitby was down to 300 by 1884. While jet substitutes may have had an impact this appears to have been in a large part due to changes in fashion with
Art Nouveau Art Nouveau (; ) is an international style of art, architecture, and applied art, especially the decorative arts. The style is known by different names in different languages: in German, in Italian, in Catalan, and also known as the Modern ...
making little use of black jewellery. As the numbers fell the remaining manufactures tended to stick with existing styles rather than attempting to adapt to new fashions resulting in demand falling further. Making tourist trinkets kept a few jewellers in work but by the end of World War II only 3 remained and the industry died out completely with their deaths.


20th century

In Whitby the Victorian tradition continued up until the aftermath of World War II. Jet Jewellery (both vintage and new) was then to remain out of fashion until the late 70s. In the 80s there was a fashion for Jet beads and antique jet jewellery started to rise in value. New jewellers took up the production of Jet Jewellery.


Jet substitutes

Glass was used as a jet substitute during the peak of jet's popularity. When it was used in this way it was known as French jet or Vauxhall glass. Ebonite was also used as a jet substitute and initially looks very similar to jet, but it fades over time. In some cases jet offcuts were mixed with glue and molded into jewelry.
Anthracite Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...
(hard
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
) is superficially similar to fine jet, and has been used to imitate it. This imitation is not always easy to distinguish from real jet. Some museums have produced reproductions of jet artefacts in
epoxy resin Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional ...
.


Authenticating jet

Unlike black
glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...
, which is cool to the touch, jet is not cool, due to its lower
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
. When rubbed against unglazed porcelain, true jet will leave a brown streak, although bog oak, vulcanite and
lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...
will do the same. When non destructive testing is required
X-ray fluorescence spectroscopy X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...
combined with visual inspection (including under high magnification) and X-ray imaging is generally effective although it can be difficult to differentiate jet from lignite Real jet, when placed in a flame, burns like coal and gives off a coal-like smell and produces
soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed ...
. No other black "gemstone" behaves like this.


See also

* Petrified wood *
Oltu stone Oltu stone ( tr, Oltu taşı) is a kind of jet found in the region around Oltu town within Erzurum Province, eastern Turkey. The organic substance is used as semi-precious gemstone in manufacturing jewellery. Location and extraction Oltu stone, ...


References


External links


Gemstone Guide: Jet

Roman Objects in the Yorkshire Museum
{{DEFAULTSORT:Jet (Lignite) Coal Organic gemstones Sedimentology jet