Manganosites

Manganosite is a rare mineral composed of manganese(II) oxide, with the chemical formula MnO. It is a member of the cubic oxide mineral group. Manganosite typically occurs as small, euhedral to anhedral crystals or as granular masses. Its color can range from grayish-black to greenish-black. It is relatively soft, with a Mohs hardness of about 5 to 6, and has a moderate specific gravity.

Manganosite is found in metamorphic rocks, particularly in metamorphosed manganese deposits, where it forms under low to moderate oxygen fugacity conditions. It is often associated with other manganese minerals such as rhodonite, bustamite, hausmannite, and spessartine. It can also be found in some skarns and volcanic rocks. Notable occurrences include Langban in Sweden, Långban in Sweden, and Franklin and Sterling Hill in New Jersey, USA.

The mineral is an important indicator of specific metamorphic conditions. Due to its rarity and the small crystal sizes often encountered, manganosite is not a significant ore of manganese. However, it is of interest to mineral collectors and geologists studying metamorphic petrology and mineral paragenesis. Its transformation to other manganese oxides like hausmannite can occur with further oxidation.