Quartz is the mineral species of amethyst and citrine. It is silicon dioxide in a trigonal crystal.
In more detail
Quartz has a refractive index of 1.544 to 1.553, a specific gravity of 2.65 and a hardness of 7. Its low refractive index needs a steep pavilion. Quartz turns the plane of polarized light, so its conoscope figure is a bull's-eye. Laboratories grow quartz only by the hydrothermal method.
On a grading report
Labs print 'quartz' as the identification and the variety, such as amethyst or citrine.
Related terms
- Amethyst: Amethyst is the purple variety of quartz. Iron in the crystal, together with natural radiation, causes its color.
- Citrine: Citrine is the pale yellow to brownish orange variety of quartz.
- Ametrine: Ametrine is quartz that is part amethyst and part citrine: purple and yellow zones in one crystal.
- Hydrothermal growth: Hydrothermal growth makes synthetic crystals in a hot water solution under high pressure.
- Gem species: A gem species is a mineral with one chemical composition and one crystal structure, such as corundum, beryl or quartz.