Braunite

braunite [′brau̇‚nīt]

(mineralogy)

3Mn₂O₃·MnSiO₃Brittle mineral that forms tetragonal crystals; commonly found as steel-gray or brown-black masses in the United States, Europe, and South America; it is an ore of manganese.

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Braunite 

(after the 19th-century German scientist M. Braun), a mineral of the group of compound oxides. Its chemical composition is complex and is expressed approximately by the formula Mn²⁺Mn₆³⁺SiO₁₂. It crystallizes in a tetragonal system, forming crystals of dipyramidal habit. It is most often found in the form of compact, granular aggregates. The color is black; the luster is matte and semimetallic. Braunite’s hardness on the mineralogical scale is 6.0-6.5; its density is 4, 700-5, 000 kg/m³. It is sometimes weakly magnetic.

Braunite is found in hydrothermal veins and in contact-metamorphic formations. The largest ore beds are in regionally metamorphized and contact-metamorphized sedimentary deposits that are rich in manganic oxides. Braunite is unstable and is easily converted to psilomelane and pyrolusite. Braunite is one of the most important manganese ores used for extracting ferromanganese. The largest deposits of braunite are in India; in the USSR it is found in Kazakhstan.