Citrine (quartz)
| Citrine | |
|---|---|
Cut citrine from Brazil | |
| General | |
| Category | Tectosilicates, quartz variety |
| 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 | aluminum, 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. It is sometimes used as a modern, more affordable alternative to the traditional November birthstone, topaz. Not every yellow quartz is considered citrine, and there is disagreement as to when the name "citrine" is appropriately used. However, quartz stained by iron inclusions or coatings is generally not considered citrine.
Natural citrine is rare; most commercially available citrine is produced by heating amethyst or smoky quartz. Natural citrine tends to have a pale yellow, often smoky color, while heat-treated amethyst is typically a deeper yellow, orange, red, or even brown ("burnt amethyst").