Stannite

Formula: Cu₂FeSnS₄

Origin of name: from compositon (Latin stannum = tin)

Crystal system: tetragonal

Crystal class: -42m

Twinning: on {102} penetration, also on {112} about [112] axis

Unit cell: a = 5.453 Å, c = 10.75 Å

Colour: steel-gray to grayish black, tarnishes blue

Diaphaneity: 

Luster: metallic

Habit: crystals pseudotetragonal or pseudododecahedral due to twinning, often striated, massive, granular

Hardness: 4

Specific gravity: 4.3 to 4.5

Cleavage: 2; {110} and {001} indistinct

Tenacity: uneven, brittle

Streak: blackish

Synonyms/varieties:

Comments: dimorphous with ferrokesterite