Alleghanyite

Formula:  Mn₅(SiO₄)₂(OH)₂

Origin of name:  Locality; Alleghany Co., North Carolina, USA

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning: On {001}, lamellar, common; also on {105}, {305}

Unit cell: a = 8.275 Å, b = 4.850 Å, c = 10.720 Å, b = 104.64°

Colour:  Brown to pinkish brown to deep pink

Diaphaneity: Transparent to translucent.

Luster:  Vitreous to dull.

Habit:  Crystals slender plate-like, deeply striated by twinning or unstriated  stout platy crystals; usually massive or irregular grains.

Hardness:  5.5

Specific gravity:  4.02 

Cleavage:  None

Tenacity: Brittle

Streak:

Synonyms/varieties:

Comments:  Dimorphous with ribbeite. Member of the humite group. Hydrothermally deposited, in lenses in a manganese-bearing vein, in veins crosscutting franklinite ore near pegmatites in a metamorphosed stratiform Zn-Mn deposit