Citrine (quartz)
| Citrine | |
|---|---|
Cut citrine from Brazil | |
| General | |
| Category | Tectosilicate minerals |
| Group | Quartz group |
| Formula | Silica (silicon dioxide, SiO2) |
| IMA symbol | Qz |
| IMA status | Variety of quartz |
| 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 | |
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). 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.