Citrine is a transparent, yellow variety of quartz. Its name is derived from the Latin word citrus (citron tree), by way of the French citrin or citron (lemon).[3] Citrine is one of the most popular yellow gemstones and has been used since ancient 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 heating amethyst or smoky quartz.
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 aluminum-based color centers in its crystal structure, similar to smoky quartz.[4][5] Citrine and smoky quartz occur in the same geological environments and can frequently be found together in the same crystal as smoky citrine. Alternatively, it has been suggested that the color of citrine may be due to trace amounts of iron;[2] many sources claim iron 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 or dichroism of natural citrine. The ultraviolet 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-treated amethyst[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 as burnt amethyst.[9] Unlike natural citrine, the color of heat-treated amethyst is known to come exclusively from trace amounts of iron oxides, specifically hematite and goethite. 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 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 produce madeira citrine, which has a deep orange color and exhibits red flashes. Its name comes from madeira, the Brazilian word for wood.[7] Clear quartz can also be irradiated to produce lemon quartz, which has a neon yellow to yellow-green color.[1]
Differentiation
Quartz from Brazil with visible surface staining, sometimes incorrectly identified as citrine
Clear quartz with natural iron inclusions or limonite 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]
Heat-treated amethyst geode showing color zoning
Like natural amethyst, heat-treated amethyst often exhibits color zoning, or uneven color distribution, throughout the crystal.[10] In geodes 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]
Cut yellow topaz, which resembles citrine in color
It can be difficult to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. All quartz varieties have a hardness of 7 on the Mohs scale, while topaz has a hardness of 8.[13]
Citrine can also be difficult to distinguish from yellow scapolite, 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 higher birefringence.[14]
Quartz and its varieties have been used as gemstones for thousands of years. Citrine and other quartzes are believed to have been used by the ancient Egyptians to make talismans, by the ancient Greeks for carving symbols, and by Roman priests as rings. Queen Victoria was reportedly fond of the gemstone; many brooches and pendants 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 name topaz for any golden yellow stone. The name citrine 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 November birthstone, yellow topaz.[13]
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