Diamond

Formula:  C

Origin of name:  From Greek for invincible

Crystal system:   Cubic

Crystal class:   4/m -3 2/m

Twinning:  Common on {111}, contact or penetration, sometimes repeated

Unit cell: a = 3.567 Å

Colour:   Colourless, white to blue-white, gray, yellow, brown, green

Diaphaneity: Transparent to translucent

Luster:  Adamantine to greasy 

Habit:   Crystals octahedral, or cubic, dodecahedral, tetrahedral; flattened, faces curved or striated, spherical aggregates

Hardness:   10

Specific gravity:   3.51

Cleavage:   1; {111} perfect

Tenacity:   Conchoidal fracture; brittle

Streak: 

Synonyms/varieties:  Carbonado (black massive var.), bort (grey massive variety)

Comments:   Dimorphous with chaoite, graphite, and lonsdaleite; sometimes fluoresces and phosphorescence, triboelectric, highest thermal conductivity of any known substance. Primarily formed in pipes, less often in dikes, of deep-seated igneous origin, composed of kimberlite or lamproite. Also found in alluvial deposits.