Pyrolusite
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| Pyrolusite | |
|---|---|
 Pyrolusite Mineral with Dendrite (height of sample ~9 cm)
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| General | |
| Category | Mineral |
| Chemical formula | manganese dioxide, MnO2 |
| Identification | |
| Color | Darkish, black to lighter grey, somethimes bluish |
| Crystal habit | Granular to massive - botryoidal and dendritic |
| Crystal system | Tetragonal |
| Cleavage | Perfect on 100 and 011 |
| Fracture | Rough |
| Mohs Scale hardness | 2 - 2.5 |
| Luster | Metallic |
| Refractive index | Opaque |
| Pleochroism | None |
| Streak | Same as color |
| Specific gravity | 4.73 - 4.86 |
| Major varieties | |
| Polianite | Massive crystals of the very pure form |
Pyrolusite is a mineral consisting essentially of manganese dioxide (MnO2) and is important as an ore of manganese. It is a soft, black, amorphous appearing mineral, often with a granular, fibrous or columnar structure, sometimes forming reniform crusts. It has a metallic luster, a black or bluish-black streak, and readily soils the fingers. The specific gravity is about 4.8.
Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminium, or by electrolysis. Pyrolusite is extensively used for the manufacture of spiegeleisen and ferromanganese and of various alloys such as manganese-bronze. As an oxidizing agent it is used in the preparation of chlorine and disinfectants (permanganates) and for decolorizing glass. When mixed with molten glass it oxidizes the ferrous iron to ferric iron, and so discharges the green and brown tints. As a coloring material, it is used in calico printing and dyeing; for imparting violet, amber and black colors to glass, pottery and bricks; and in the manufacture of green and violet paints.
[edit] Variations in crystal habit
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
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