Clausthalite

Formula:  PbSe

Origin of name:  Locality; Clausthal, Germany

Crystal system:  Cubic

Crystal class:  4/m -3 2/m

Twinning:

Unit cell: a = 6.1243 Å

Colour:  Bright lead-gray;

Diaphaneity:  Opaque

Luster:  Metallic

Habit:  Massive, fine grained, foliated

Hardness:  2.5 to 3

Specific gravity:  8.08 to 8.22

Cleavage:  1; {001} good

Tenacity: Brittle, granular fracture

Streak:  Greyish black

Synonyms/varieties:

Comments:  Series with galena. Found in association with other selenides in low sulphur hydrothermal deposits, also in mercury deposits. Probably of secondary origin in some deposits.