The name "Citrine" (Citrin German, Topacio falso Spanish, Citrino Italian) comes from the French word "citron," or "lemon," for its color. Citrine closely resembles topaz (also a birthstone for November), but is slightly softer, and has less brilliance. Citrine has been used in Greece since the Hellenistic period at the end of the 4th to the end of the 1st century BC. Citrine can permanently change color if left in direct sunlight for several hours. In ancient times, citrine was carried as a protection against snake venom. It is also thought to aid digestion, and remove toxins from the body.
Citrine has a hardness of 7 to 7 1/2 on the Mohs scale. The Toughness of Citrine is Good. Citrine crystallizes in the trigonal crystal system and/or hexagonal crystal system (trigonal-trapezohedral), with an "Enantiomorphic" crystal habit. Citrine has a glassy to Vitreous luster, and a refractive index of 1.550. Citrine's cleavage is weak in three directions (rhombohedral).
Primary sources for citrine are found in Brazil, Madagascar, and Sri Lanka. Citrine is a coarse-grained, transparent variety of the Tectosilicate silica mineral quartz. The yellow color in natural citrine is derived from the presence of iron. The darker the color of the citrine, the higher the grade. Cryptocrystalline varieties of citrine can be multicolored.
Naturally occurring citrine derives its golden color from the presence of iron (Fe3) ions. Purple amethyst will turn to citrine when heated in a kiln for a certain period of time and much of the yellow, gold, or orange citrine on the market today is heat-treated amethyst.
Chemical composition: SiO2
Ametrine
A rare and unique bi-colored variation of citrine and amethyst is the recent discovery of a naturally occurring gemstone called Ametrine. Ametrine is a variety of quartz that contains both amethyst and citrine colored by trace elements of Fe3 (citrine yellow) and Fe4 (amethyst purple) iron ions. At present, the only major source for Ametrine is from the Anahí Mine in Santa Cruz, Bolivia. This stone has a color transition that is similar to tourmaline, but with the distinct amethyst purple and citrine gold colors. There is also a synthetic Ametrine that is being manufactured in Alexandrov, Russia
Further Reference on Ametrine:
Caltech - Ametrine
