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Amethyst

Mineral, quartz variety / From Wikipedia, the free encyclopedia

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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.

Quick facts: Amethyst, General, Category, Formula .mw-pars...
Amethyst
Amatista_Laye_2.jpg
Amethyst cluster from Artigas, Uruguay
General
CategorySilicate mineral
Formula
(repeating unit)
Silica (silicon dioxide, SiO2)
Crystal systemTrigonal
Crystal classTrapezohedral (32)
Space groupP3221 (no. 154)
Identification
ColorPurple, violet, dark purple
Crystal habit6-sided prism ending in 6-sided pyramid (typical)
TwinningDauphine law, Brazil law, and Japan law
CleavageNone
FractureConchoidal
Mohs scale hardness7–lower in impure varieties
LusterVitreous/glassy
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.65 constant; variable in impure varieties
Optical propertiesUniaxial (+)
Refractive indexnω = 1.543–1.553
nε = 1.552–1.554
Birefringence+0.009 (B-G interval)
PleochroismWeak to moderate purple/reddish purple
Melting point1650±75 °C
SolubilityInsoluble in common solvents
Other characteristicsPiezoelectric
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Amethyst, a semiprecious stone, is often used in jewelry.