Bementite

Formula:  Mn₈Si₆O₁₅(OH)₁₀

Origin of name:  For Clarence Bement (1843-1923), American mineral collector of Philadelphia

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 14.838 Å, b = 17.584 Å, c = 14.7 Å, b = 95.54°

Colour:  Brown, yellow, gray; darkens on exposure

Diaphaneity:  Translucent

Luster:  Waxy, pearly on cleavage

Habit:  Crystals, radiated or stellate; massive, granular

Hardness:  6

Specific gravity:  2.9 to 3.10

Cleavage:  3; {001} perfect micaceous, {010} and {110} perfect

Tenacity: Conchoidal fracture

Streak:

Synonyms/varieties:

Comments: Found in layers parallel to the walls of secondary veins of calcite in metamorphosed stratiform Zn-orebody, intimately intergrown with other manganese minerals