Cristobalite

Formula:  SiO₂

Origin of name:  Locality; Cerro San Cristobal Pachuca, Mexico

Crystal system:  Tetragonal

Crystal class:  422

Twinning:  Common on {111}, penetration or polysynthetic

Unit cell: a = 4.971 Å, c = 6.918 Å

Colour:  White, gray, bluish-gray, yellowish, brownish

Diaphaneity: 

Luster:  Vitreous

Habit:  Crystals pseudo-octahedral or rarely pseudo-cubic, small; massive; stalactitic, spherulitic, crusts or botryoidal

Hardness:  6.5

Specific gravity:  2.33

Cleavage:  None

Tenacity:  Brittle

Streak:

Synonyms/varieties:

Comments:  Polymorphous with coesite, quartz, stishovite and tridymite