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Quartz
Quartz crystal cluster from Brazil
General
Category	Silicate mineral[1]
Formula (repeating unit)	SiO2
IMA symbol	Qz[2]
Strunz classification	4.DA.05 (oxides)
Dana classification	75.01.03.01 (tectosilicates)
Crystal system	α-quartz: trigonal β-quartz: hexagonal
Crystal class	α-quartz: trapezohedral (class 3 2) β-quartz: trapezohedral (class 6 2 2)[3]
Space group	α-quartz: P3221 (no. 154)[4] β-quartz: P6222 (no. 180) or P6422 (no. 181)[5]
Unit cell	a = 4.9133 Å, c = 5.4053 Å; Z = 3
Identification
Formula mass	60.083 g·mol−1
Color	Colorless, pink, orange, white, green, yellow, blue, purple, dark brown, or black
Crystal habit	6-sided prism ending in 6-sided pyramid (typical), drusy, fine-grained to microcrystalline, massive
Twinning	Common Dauphine law, Brazil law, and Japan law
Cleavage	{0110} Indistinct
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	7 – lower in impure varieties (defining mineral)
Luster	Vitreous – waxy to dull when massive
Streak	White
Diaphaneity	Transparent to nearly opaque
Specific gravity	2.65; variable 2.59–2.63 in impure varieties
Optical properties	Uniaxial (+)