Freibergite

Formula:  (Ag,Cu,Fe)₁₂(Sb,As)₄S₁₃

Origin of name:  After locality; Freiberg, Saxony, Germany

Crystal system:  Cubic

Crystal class:  -43m

Twinning:

Unit cell:

Colour:  Steel-gray to iron-black

Diaphaneity:  Opaque

Luster:  Metallic

Habit:  Crystals tetrahedral; massive, coarse granular to compact

Hardness:  3 to 4.5

Specific gravity:  5.05

Cleavage:  None

Tenacity:

Streak:  Streak black to brown

Synonyms/varieties:

Comments:  Series with argentotennantite and with tetrahedrite