pyrolusite (pĪˈrōlōzĪt) [key], 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.
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