Coombsite

Formula:  KMn₁₃(Si,Al)₁₈O₄₂(OH)₁₄

Origin of name:  For Douglas Coombs, mineralogist of New Zealand

Crystal system:  Hexagonal

Crystal class:  3 or -3

Twinning:

Unit cell:

Colour:  Brown

Diaphaneity:  Semitransparent

Luster:

Habit:  Fibro-lamellar crystals to 20 µm long in patchy aggregates a few mm across

Hardness:

Specific gravity:  3.0

Cleavage:  None

Tenacity:

Streak:

Synonyms/varieties:

Comments:  Manganese analogue of zussmanite