Manganite

Manganite, the hydrous sesquioxide of manganese, an ore of manganese and a source of oxygen, though, owing to its smaller percentage (275) of oxygen, of less value in the latter application than pyrolusite (q.v.). It occurs in sub-metallic, iron-black crystals, which are rhombic prisms, and has a hardness of 4 and specific gravity of about 4-3. It is found at various places in Cornwall, the Mendip Hills and elsewhere.