Braunite

Formula:  MnMn₆SiO₁₂

Origin of name:  For Kammerrath (advisor of the Chamber) Braun of Gotha, Germany

Crystal system:  Tetragonal

Crystal class:  4/m 2/m 2/m

Twinning: on {112}

Unit cell: a = 9.36-9.45 Å, c = 18.60-18.97 Å

Colour:  Brownish-black, black, steel-gray

Diaphaneity:  Opaque

Luster:  Submetallic

Habit:  Crystals pyramidal, striated; massive, granular

Hardness:  6 to 6.5

Specific gravity:  4.72 to 4.83

Cleavage:  1; {112} perfect

Tenacity: Brittle, uneven to subconchoidal fracture

Streak:  Brownish black to steel-gray

Synonyms/varieties:

Comments: Forms a series with abswurmbachite. Formed metamorphism of manganese silicates and oxides, also a product of weathering.