Braunite


Also found in: Dictionary, Medical, Wikipedia.

braunite

[′brau̇‚nīt]
(mineralogy)
3Mn2O3·MnSiO3 Brittle 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.

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.

Mentioned in ?
References in periodicals archive ?
No significant mineral finds have been reported from those localities, except for braunite and manganese oxides.
Braunite forms the main part of the manganese ore in all the Val Graveglia mines, as layers within chert and as large masses up to 20 meters in thickness.
The better specimens are undoubtedly those from the Cassagna mine, with pale green prismatic crystals up to 2 mm, sometimes associated with braunite, calcite, piemontite and barite crystals.
Tabular, black and very lustrous crystals were found at the Gambatesa mine in the fractures in braunite and at the Molinello mine in vugs in rhodonite veins (Palenzona, 1987), at the same time that tangeite was collected.
The specimens from the Molinello mine, with crystals up to 1 cm, in rhodonite cavities or in the quartz veins that cut the braunite ore, are the best in the world.
It occurred very sparingly at the surface of cavities and fractures in a manganese ore containing tephroite, bementite, braunite, hausmannite and hematite.
Zeolite crystals visually identifiable as phillipsite or harmotome are well-known as last-formed minerals in carbonate veins, braunite fractures and tinzenite druses (Antofilli et al.
A close examination of the color can be a clue: usually hausmannite is dark brown while braunite is black.
The best, with sharp, lustrous crystals up to 3 mm, were collected at the beginning of the 1990's in braunite veins, associated with carbonates, barite and, in places, phillipsite.
1978; Dunn and Leavens, 1986), and was also recognized in orange to yellow crystals up to 2 mm from the Molinello mine, associated with braunite, barite and calcite (Palenzona, 1987b).
This mineral was originally studied in braunite ore collected at the Molinello mine, consisting of veinlets in the braunite ore in which medaite was associated with quartz, calcite, ganophyllite and another new species, tiragalloite.
In 1988 good prismatic, bright red crystals were found, again at Molinello mine, on braunite in a quartz vein.