Enargite

Formula:   Cu₃AsS₄

Origin of name:   From Greek for distinct

Crystal system:   Orthorhombic

Crystal class:   mm2

Twinning:   Common on {320}, occasionally as trillings

Unit cell: a = 6.431 Ǻ, b = 7.402 Ǻ, c = 6.149 Ǻ

Colour:  Grayish black to iron-black

Diaphaneity:

Luster:   Metallic

Habit:   Crystals prismatic or tabular; massive, granular or prismatic

Hardness:   3

Specific gravity:   4.45

Cleavage:   4; {110} perfect, {100} and {010} distinct, {001} indistinct

Tenacity:   Uneven; brittle

Streak:   Grayish black

Synonyms/varieties:

Comments:   Dimorphous with luzonite