Tetrahedrite

Formula: (Cu,Fe)₁₂Sb₄S₁₃

Origin of name: from tetrahedral form of the crystal

Crystal system: cubic

Crystal class: -43m

Twinning: on {111}, contact or penetration

Unit cell: a = 10.33 Å

Colour: steel-gray to iron-black

Diaphaneity: 

Luster: metallic, sometimes splendent

Habit: crystals tetrahedral, modified, massive, coarse granular to compact

Hardness: 3 to 4.5

Specific gravity: 4.6 to 5.1

Cleavage: none

Tenacity: subconchoidal to uneven, brittle

Streak: black to brown

Synonyms/varieties: annivite (Bi-rich variety), fahlerz, fahlore, panabase

Comments: series with tennantite and with freibergite