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Color: Clear (if no impurities); also see Varieties Crystal: habit 6-sided prism ending in 6-sided pyramid (typical) Crystal system: Hexagonal rhombohedral class 32 Twinning Dauphine law, Brazil law and Japan law Cleavage: None Fracture: Conchoidal Mohs Scale hardness 7 - lower in impure varieties Luster: Vitreous/glossy Refractive index nω = 1.543 - 1.545 nε = 1.552 - 1.554 Optical Properties Uniaxial (+) Birefringence +0.009 (B-G interval) Pleochroism: None Streak: White Specific gravity: 2.65 constant; variable in impure varieties Melting point :1650 (±75) °C Solubility :H2O insoluble Diaphaneity: Transparent to translucent Other Characteristics: Piezoelectric
Quartz Chemical composition: SiO2 Class: tectosilicate Crystal system: Hexagonal-R; 32 (trigonal-trapezohedral) Crystal habit: Macroscopic crystals commonly occur as horizontally striated hexagonal prisms terminated by a combination of positive and negative rhombohedrons forming six sided pyramids. Prism faces and/or rhombohedral terminations may be lacking, poorly developed or predominant resulting in diverse possible crystal habits. Trigonal tapezohedral faces can occur in the upper right or left of alternating prism faces identifying right or left handed crystals, respectively. Quartz also occurs in crystalline and microcrystalline massive forms of great variety. Twinning: Dauphine twin with c the twin axis, Brazil twin with {1120} the twin plane, Japanese twin is rare with {1122} the twin plane. Specific gravity: macrocrystalline varieties 2.65, cryptocrystalline 2.58-2.91 Index of refraction: macrocrystalline varieties 1.54-1.55, cryptocrystalline 1.53-1.55 Birefringence: weak, maximum of 0.009 Pleochroism: most colored varieties show dichroism Hardness: macrocrystalline varieties 7, cryptocrystalline 6.5 to 7 Color: normally colorless or white, but frequently colored by impurities and then may be any color. Luster: vitreous, can be greasy Transparency: transparent to translucent Cleavage: quartz varieties seldom show cleavage although several difficult cleavages do exist in quartz. Massive pegmatite or vein quartz may show distinct rhombohedral {1011} cleavage. Cryptocrystalline quartz shows no cleavage, although parting may occur along layers and splintery fracture can develope parallel to microfibrous orientation. Fracture: conchoidal Streak: white Electrical properties: rock crystal quartz is strongly piezoelectric and pyroelectric
