| Citrine | |
|---|---|
 Cut citrine from Brazil | |
| General | |
| Category | Tectosilicateminerals,quartzvariety |
| Formula | Silica (silicon dioxide,SiO2) |
| IMA symbol | Qz |
| Strunz classification | 4.DA.05 (Oxides) |
| Dana classification | 75.1.3.1 (Tectosilicates) |
| Crystal system | Trigonal |
| Crystal class | Trapezohedral (class 3 2) |
| Identification | |
| Color | Natural: pale yellow, with orange, green, or smoky hues Heat-treated amethyst: yellow-orange, orange-red, orange-brown |
| Crystal habit | Hexagonal, massive Heat-treated amethyst only: druzy, geodes |
| Twinning | Common: Dauphiné Law, Brazil Law, Japan Law |
| Cleavage | None |
| Fracture | Conchoidal |
| Mohs scale hardness | 7 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.65 |
| Optical properties | Uniaxial (+) |
| Refractive index | 1.544-1.553 |
| Birefringence | 0.009 |
| Pleochroism | Natural: weak dichroism (different shades of yellow or orange) Heat-treated amethyst: none |
| Dispersion | 0.013 |
| Common impurities | aluminium,iron |
| References | [1][2] |
Citrine is a transparent, yellow variety ofquartz. Its name is derived from the Latin wordcitrus (citron tree), by way of the Frenchcitrin orcitron (lemon).[3] Citrine is one of the most popular yellowgemstones and has been used sinceancient Egyptian times. There is disagreement as to which trace elements are responsible for its color. Not all yellow quartz is considered citrine, such as quartz stained by iron inclusions or coatings. Natural citrine is rare; most commercially available "citrine" is produced by heatingamethyst orsmoky quartz.
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Natural citrine ranges in color from yellow to yellow-orange or yellow-green. The causes of its color are not well agreed upon.[2] Evidence suggests the color of citrine is linked to the presence of aluminium-basedcolor centers in its crystal structure, similar tosmoky quartz.[4][5] Citrine and smoky quartz occur in the same geological environments and can frequently be found together in the same crystal assmoky citrine. Alternatively, it has been suggested that the color of citrine may be due to trace amounts of iron;[2] many sources claimiron oxides as the source of citrine's color.[1][6][7] However, synthetic crystals grown in iron-rich solutions have failed to replicate the color ordichroism of natural citrine. Theultraviolet sensitivity of natural citrine further indicates that its color is not caused solely by trace elements.[2]
Citrine is very rare in nature; most "citrine" on the market is actually heat-treatedamethyst[6][2] and is therefore not true citrine according the strict mineralogical definition.[2] Amethyst loses its natural violet color when heated to above 200–300 °C (392–572 °F).[8] Natural citrine tends to be pale in color, while heat-treated amethyst is typically a deeper yellow, orange, red, or even brown;[1] the latter is sometimes referred to asburnt amethyst.[9] Unlike natural citrine, the color of heat-treated amethyst is known to come exclusively from trace amounts of iron oxides, specificallyhematite andgoethite. This iron was present in the original amethyst and oxidized by the heating process. Heat-treated amethyst, like synthetic crystals, does not exhibit the dichroism of natural citrine. Smoky quartz can also be heat treated to resemble citrine; smoky quartz is naturally dichroic, and heat-treated smoky quartz retains its dichroism.[2]
Amethyst with a certain iron content can be heated to producemadeira citrine, which has a deep orange color and exhibits red flashes. Its name comes frommadeira, the Brazilian word for wood.[7] Clear quartz can also be irradiated to producelemon quartz, which has a neon yellow to yellow-green color.[1]
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Clear quartz with natural iron inclusions orlimonite staining may resemble citrine. However, these crystals will either have coloration only on the surface or in certain spots (inclusions) within the crystal. Quartz that derives its color from coatings or inclusions is not considered citrine.[2]
Like natural amethyst, heat-treated amethyst often exhibits color zoning, or uneven color distribution, throughout the crystal.[10] Ingeodes and clusters, the color is usually deepest near the tips and white or clear near the base.[8] Unlike heat-treated amethyst, natural citrine does not occur in geodes or large clusters. Natural citrine typically exhibits fairly even coloration throughout the crystal, and it will never contain opaque white quartz.[11][12]
It can be difficult to differentiate between cut citrine and yellowtopaz visually, but they differ in hardness. All quartz varieties have a hardness of 7 on theMohs scale, while topaz has a hardness of 8.[13]
Citrine can also be difficult to distinguish from yellowscapolite, although citrine is much more common as a gemstone.[1] They can be distinguished by their pleochroism: citrine is weakly dichroic, while scapolite is moderately to strongly pleochroic. Scapolite also usually has higherbirefringence.[14]
Most citrine, both natural[1] and heat-treated amethyst,[13] originates from Brazil. Natural citrine can also be found in Russia andMadagascar.[13]Uruguay,Zambia, Madagascar, and the Brazilian state ofRio Grande do Sul are the leading producers ofmadeira citrine.[7] Other notable sources of citrine includeBolivia, theDemocratic Republic of the Congo, Mexico,Myanmar,Namibia,Peru,South Africa, and the United States.[1]
Quartz and its varieties have been used as gemstones for thousands of years. Citrine and other quartzes are believed to have been used by theancient Egyptians to make talismans, by theancient Greeks for carving symbols, and byRoman priests as rings.Queen Victoria was reportedly fond of the gemstone; manybrooches andpendants featuring citrine survive from this era.[15] In the centuries before modern mineralogy, citrine was frequently confused with topaz. It was common in many cultures to use the nametopaz for any golden yellow stone. The namecitrine was first used in English in the 14th century.[16] Citrine has been referred to as the "merchant's stone" or "money stone", due to a superstition that it would bring prosperity.[17]
Today, citrine is the top-selling yellow-orange gemstone,[6] and it is commonly used in jewelry. It has become more popular over the last few decades due to aggressive marketing tactics and earth-tone fashion trends.[1] Citrine is sometimes used as a modern, more affordable alternative to the traditional Novemberbirthstone, yellowtopaz.[13]
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| Notable varieties |
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Gemmological classifications by E. Ya. Kievlenko (1980), updated | |||||||||
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