Akhtenskite

Formula: MnO₂

Origin of name:  For locality; Akhtenskoye deposit, Urals, Russia

Crystal system:  Hexagonal

Crystal class:  6/m 2/m 2/m

Twinning:

Unit cell: a = 2.83-2.85 Å, c = 4.47-4.88 Å

Colour:  Light gray to black

Diaphaneity: Opaque

Luster:

Habit:  Platy aggregates, microscopic crystals with flaky to platy habit

Hardness:

Specific gravity:  4.78 (calculated)

Cleavage: 1; {001}

Tenacity:

Streak: Black

Synonyms/varieties:

Comments:  Structural analogue of feroxyhyte; trimorphous with pyrolusite and ramsdellite. Observed in mixtures in "psilomelane" with other manganese oxides in iron oxide deposits. Probably bacterially altered from a previous mineral; in incrustations of ferromanganese minerals on oceanic basalt on a guyot.