pyrolusite

A soft, black to dark gray mineral, MnO₂, the commonest and most important secondary ore of manganese.

Native manganese dioxid (MnO₂), a common ore of manganese, occurring crystallized and massive, of a gray-color and metallic luster.

Manganese dioxide, a mineral of an iron-black or dark steel-gray color and metallic luster, usually soft. Pyrolusite parts with its oxygen at a red heat, and is extensively used in discharging the brown and green tints of glass (whence its name).

A dark coloured mineral, consisting of manganese dioxide (MnO2), that is an important ore of manganese.

a mineral consisting of manganese dioxide; an important source of manganese