Amethyst | |
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![]() Amethyst cluster from Artigas, Uruguay | |
General | |
Category | Silicate mineral |
Formula (repeating unit) | Silica (silicon dioxide, SiO2) |
Crystal system | Trigonal |
Crystal class | Trapezohedral (32) |
Space group | P3221 (no. 154) |
Identification | |
Color | Purple, violet, dark purple |
Crystal habit | 6 sided prism ending in 6 sided pyramid (typical) |
Twinning | Dauphine law, Brazil law, and Japan law |
Cleavage | None |
Fracture | Conchoidal |
Mohs scale hardness | 7 (lower in impure varieties) |
Luster | Vitreous/glassy |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 2.65 constant; variable in impure varieties |
Optical properties | Uniaxial (+) |
Refractive index | nω = 1.543–1.553 nε = 1.552–1.554 |
Birefringence | +0.009 (B-G interval) |
Pleochroism | Weak to moderate purple/reddish purple |
Melting point | 1650±75 °C |
Solubility | Insoluble in common solvents |
Other characteristics | Piezoelectric |
Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω (Ancient Greek) methysko / μεθώ metho (Modern Greek), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness.[1] Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Amethyst, a semiprecious stone, is often used in jewelry.
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