Ramsdellite

Formula: MnO₂

Origin of name: for L. Ramsdell, American mineralogist

Crystal system: orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning:

Unit cell: a = 4.533 Å, b = 9.27 Å, c = 2.866 Å

Colour: steel-gray to iron-black

Diaphaneity: opaque

Luster: brilliant metallic

Habit: pseudomorphs of groutite crystals, massive, platy or finely crystalline

Hardness: 2 to 4

Specific gravity: 4.37 to 4.83

Cleavage: 4; three on pinacoids, one on prism

Tenacity: 

Streak: dull black

Synonyms/varieties:

Comments: trimorphous with pyrolusite and akhtenskite