Chrysoprase, chrysophrase or chrysoprasus 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, ...

variety of

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 monocli ...

cryptocrystalline Cryptocrystalline is a 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 and flint are crypt ...

form of

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

) that contains small quantities of

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

. Its color is normally apple-green, but varies to deep green. The darker varieties of chrysoprase are also referred to as prase. (However, the term prase is also used to describe

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorou ...

-included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.) Chrysoprase is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystal,

amethyst Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος ''amethystos'' from α- ''a-'', "not" and μεθύσκω (Ancient Greek) / μεθώ (Modern Greek), "intoxicate", a reference to the belief that ...

, citrine, and the other varieties of crystalline quartz. Other members of the cryptocrystalline silica family include

agate Agate () is a common rock formation, consisting of chalcedony and quartz as its primary components, with a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Anci ...

carnelian Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker (the difference is not rigidly defined, and the two names are often used ...

, and

onyx Onyx primarily refers to the parallel banded variety of chalcedony, a silicate mineral. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The ...

. Unlike many non-transparent silica minerals, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable. The word chrysoprase comes from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

χρυσός ''chrysos'' meaning 'gold' and πράσινον ''prasinon'', meaning 'green'. Unlike

emerald Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) ''Gemology'', John Wiley & Sons, New York, p ...

which owes its green color to the presence of

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

, the color of chrysoprase is due to trace amounts of

compounds in the form of very small inclusions. The nickel reportedly occurs as different silicates, like kerolite or

pimelite Pimelite was discredited as a mineral species by the International Mineralogical Association (IMA) in 2006, in an article which suggests that “pimelite” specimens are probably willemseite (which is approved), or kerolite (which is also discre ...

(not NiO mineral, bunsenite, as was reported before). Chrysoprase results from the deep weathering or lateritization of nickeliferous

serpentinite Serpentinite is a rock composed predominantly of one or more serpentine group minerals, the name originating from the similarity of the texture of the rock to that of the skin of a snake. Serpentinite has been called ''serpentine'' or ''s ...

s or other

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found ...

rocks. In the Australian deposits, chrysoprase occurs as veins and nodules with brown

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

and other

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of wh ...

s in the

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 ...

-rich

saprolite Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widesprea ...

below an iron and silica cap. As with all forms of

, chrysoprase has a hardness of 6–7 on the

Mohs hardness scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

and a conchoidal fracture like

flint Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start ...

. The best known sources of chrysoprase are

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, Haneti

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, and

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. Deposits in central

have been in constant production since 1986. The chrysoprase and nickel silicate ore deposit in Szklary,

Lower Silesia Lower Silesia ( pl, Dolny Śląsk; cz, Dolní Slezsko; german: Niederschlesien; szl, Dolny Ślōnsk; hsb, Delnja Šleska; dsb, Dolna Šlazyńska; Silesian German: ''Niederschläsing''; la, Silesia Inferior) is the northwestern part of the ...

, was probably the biggest European chrysoprase occurrence and possibly also the biggest in the world. A very similar mineral to chrysoprase is chrome chalcedony, in which the color is provided by

rather than nickel.

References

Gemsociety.org

External links

{{Authority control Chalcedony Quartz gemstones

See also

References

External links