PSILOMELANE

barium and manganese oxide [BaMnMn8O16(OH)4], an important ore mineral of manganese. A secondary mineral formed under surface conditions, it is often a dark gray to black alteration product of manganous carbonate or silicate minerals. It may form large residual deposits and occurs abundantly in lake or swamp bedded deposits and clays; it is also abundant as a replacement in calcareous or dolomitic rocks. It has been found in Germany, France, Belgium, Scotland, Sweden, India, and the United States. For detailed physical properties, see oxide mineral (table). The name psilomelane (from the Greek words for naked [bald, or smooth] and black) refers to the mineral's typical black, smooth-surfaced, botryoidal (grape-bunch-shaped) or stalactitic masses.