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pyrolusite(pī`rōlo͞ozīt), naturally occurring manganese dioxide, MnO2, a black mineral that crystallizes in the tetragonal system but is usually found in earthy or massive deposits. It is the principal source of manganese and its compounds, and it is extensively used in steel smelting and in the manufacture of dry-cell batteries. The main producing countries are Russia, Brazil, South Africa, Gabon, India, China, and Australia.
(also polianite), a mineral with chemical composition MnO2; contains 55–63 percent Mn. Pyrolusite crystallizes in the tetragonal system and has a rutile-type crystal structure. It rarely occurs in the form of thin columnar or acicular crystals. Most often it forms cryptocrystalline, powdery, or earthy masses combined with manganese and iron hydrous oxides, as well as with SiO2, BaO, and H2O. Pyrolusite is gray or black and has a submetallic luster. Ordinary pyrolusite has a hardness of 2–3 on Mohs’ scale, while the crystallized varieties have a hardness of up to 6. The mineral’s density varies from 4,700 to 5,080 kg/m3.
Pyrolusite is found in lacustrine or marine deposits, where oxygen is available; often commercially valuable deposits are formed. The mineral occurs in the oxidation zones of manganese deposits and in certain hydrothermal deposits.
The pyrolusite contained in manganese ores, together with psilomelane and other minerals, is used in the smelting of fer-romanganese. Pure pyrolusites are used in the manufacture of dry-cell batteries and chemical preparations and in glassmaking, porcelain manufacture, and other industries.