1) Manganese mineral 2) Mineral 3) Monoclinic mineral 
Manganite is a mineral. Its composition is manganese oxide-hydroxide, MnO(OH), crystallizing in the monoclinic system (pseudo-orthorhombic). Crystals of manganite are prismatic and deeply striated parallel to their length; they are often grouped together in bundles. The color is dark steel-grey to iron-black, and the luster brilliant and submetall...
• (n.) One of the oxides of manganese; -- called also gray manganese ore. It occurs in brilliant steel-gray or iron-black crystals, also massive. • (n.) A compound of manganese dioxide with a metallic oxide; so called as though derived from the hypothetical manganous acid.
an ore mineral of manganese, basic manganese oxide [MnO(OH)] that forms dark gray to black crystal bundles or fibrous masses. Important deposits ...
Man'ga·nite noun 1. (Min.) One of the oxides of manganese; -- called also gray manganese ore . It occurs in brilliant steel-gray or iron- black crystals, also massive. 2. (Chemistry) A compound of manganese dioxide with a metallic oxide; so called as though derived...
Manganite (grey manganese ore) is a strongly magnetic ore of manganese used in the manufacture of glass, but seldom found in commercial quantities. It is often found in veins associated with granitic igneous rocks. It alters to pyrolusite. Barite and calcite are frequent associates.
Manganese(IV) hydroxide
[n] - a black mineral consisting of basic manganese oxide
noun a black mineral consisting of basic manganese oxide; a source of manganese