Cosalite

Formula:  Pb₂Bi₂S₅

Origin of name:  Locality; Cosala mine, Sinaloa, Mexico

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning:

Unit cell: a = 19.09 Å, b = 23.87 Å, c = 4.06 Å

Colour:  Lead-gray to steel-gray to silver-white

Diaphaneity:  Opaque

Luster:  Metallic

Habit:  Crystals prismatic, may be elongated, needle-like or capillary; massive; radiating prismatic, fibrous or feathery aggregates

Hardness:  2.5 to 3

Specific gravity:  6.86 to 6.9

Cleavage:  None

Tenacity: Uneven fracture

Streak:  Black

Synonyms/varieties:

Comments: Found in moderate temperature hydrothermal deposits, but also found in contact metasomatic replacements, and epithermal replacements as well as in pegmatites.