Pyrolusite

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(Redirected from Polianite)

Pyrolusite
Pyrolusite Mineral with Dendrite (height of sample ~9 cm)
General
Category	Mineral
Chemical formula	manganese (IV) oxide, 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 ferro-manganese 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.