Amethyst

Amethyst
Amethyst
	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.

^ One or more of the preceding sentences incorporates text from a publication now in the public domain: Rudler, Frederick William (1911). "Amethyst". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 852.

[EB1911-1] One or more of the preceding sentences incorporates text from a publication now in the public domain: Rudler, Frederick William (1911). "Amethyst". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 852.

[1]