Pyrolusite - MnO₂

Habit: Usually columnar or fibrous, botryoidal, granular massive, earthy. Crystals uncommon; long to short prismatic or equant. Gray to black, black, may have a bluish cast when massive. Opaque, Metallic to earthy Luster

Environment: Formed under highly oxidizing conditions in manganese-bearing Hydrothermal deposits and rocks.

Etymology: From the Greek for fire and to wash, because it was used to decolorize the brown and green tints of glass

Primary ore of manganese. Not only is it used in the manufacturing of steel, it is used as a decolorizer in the manufacturing of glass, in electric batteries and coloring materials in bricks and pottery.