Chromium

Formula:  Cr

Origin of name:  From Greek chroma for colour, as all chromium compounds are coloured

Crystal system:  Cubic

Crystal class:  4/m -3 2/m

Twinning:

Unit cell: a = 2.8839 Å

Colour:  White, yellow tint in reflected light

Diaphaneity:  Opaque

Luster:  Metallic

Habit:  Microscopic grains

Hardness:  9

Specific gravity:  7.20

Cleavage:  None

Tenacity: Brittle (synthetic)

Streak:

Synonyms/varieties:

Comments: Found in heavy sands derived from contact metamorphic zone between a siliceous marble and ultramafic rocks