Bannisterite

Formula:  KCa(MnZn,Mg)₂₁(Si,Al)₃₂O₇₆(OH)₁₆ ^. 12H₂O)

Origin of name:  For Dr. Frederick Allen Bannister (1901- ), formerly Keeper (curator) of Minerals, British Museum (Natural History), London, England

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:

Unit cell: a = 22.265 Å, b = 16.368 Å, c = 24.668 Å, b = 94.28°

Colour:  Dark brown

Diaphaneity:  Translucent

Luster:  Resinous

Habit:  Aggregates of anhedral plates

Hardness:  4

Specific gravity:  2.83

Cleavage:  1; {001} perfect

Tenacity:

Streak:

Synonyms/varieties:

Comments: found in metamorphosed Mn-Zn orebodies