Jamesonite

Formula:  Pb₄FeSb₆S₁₄

Origin of name:  For R. Jameson, Scottish mineralogist

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  On {100}, lamellar

Unit cell: a = 15.65 Ǻ, b = 19.03 Ǻ, c = 4.03 Ǻ, β = 91.8°

Colour:  Gray-black, may tarnish iridescent

Diaphaneity: 

Luster:  Metallic

Habit:  Crystals acicular to fibrous; felt-like aggregates; columnar aggregates; massive

Hardness:  2.5

Specific gravity:  5.63

Cleavage:  1; {001} good

Tenacity:  Brittle

Streak:  Gray-black

Synonyms/varieties:

Comments:  Dimorphous with parajamesonite; series with benavidesite