Pyrolusite is an ore of manganese, and consists oheiuically of the dioxide of this metal, -Mmv.. ,It occurs in large masses, and also in rhombio crystals. It possesses a specific gravity of about-Its and a hardness of about 2-5. It was for a long time considered to be an ore of iron, arid its true nature was first demonstrated by the Swedish chemist Scheele. It was used at a very early date in glass-making (q.v.) for the purpose of decolorising glass rendered green by iron. It was formerly termed magnesia or lapis manganensis, and only incompletely distinguished from the loadstone or magncs. It is employed chemionlly as a source of oxygen and in preparation of chlorine in the manufacture of bleaching powder. It is also used in glass-making, and as a source of the manganese compounds. The principal localities where the mineral occurs are Bohemia, Spain, France, the United States and Nova Scotia, whilst sniall quantities are found in Devonshire. As obtained naturally it is seldom pure, being usually mixed with oxides of iron, nickel, and cobalt.