Quartz

Formula: SiO₂

Origin of name: from Saxon word Querkluftertz = cross-vein ore

Crystal system: hexagonal

Crystal class: 32

Twinning: very common by Dauphiné or Brazil law, less common by Japanese law, rare by several other laws

Unit cell: a = 4.91 Å, c = 5.41 Å

Colour: colourless, white, gray, yellow to brown to black, violet, pink

Diaphaneity: 

Luster: vitreous

Habit: crystals short to prismatic, elongated along c-axis, hexagonal, horizontally striated, bent, distorted, skeletal

Hardness: 7

Specific gravity: 2.655

Cleavage: 7; {10-11}, {01-11}, {10-10}, {0001}, {11-20}, {11-21}, {51-61}, seldom distinct

Tenacity: brittle

Streak: white

Synonyms/varieties:

Comments: stable below 573°C, polymorphous with tridymite, cristobalite, coesite and stishovite, actually has 7 cleavages rarely visible or distinct