Pyrolusite

Pyrolusite
Botryoidal mass of pyrolusite from Tres Cruzes, Brazil
General
Category	Oxide minerals
Formula (repeating unit)	MnO2
Strunz classification	4.DB.05
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m)
Space group	P42/mnm
Identification
Color	Darkish, black to lighter grey, sometimes bluish
Crystal habit	Granular to massive: botryoidal. Crystals rare
Twinning	{031}, {032} may be polysynthetic
Cleavage	Perfect on 110
Fracture	Brittle
Mohs scale hardness	6–6.5, 2 when massive
Luster	Metallic, dull to earthy
Streak	Black to bluish-black
Specific gravity	4.4–5.06
Refractive index	Opaque
References
Major varieties
Polianite	pseudomorphic after manganite

Pyrolusite is a mineral consisting essentially of manganese dioxide (MnO₂) and is important as an ore of manganese. It is a 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. Its name is from the Greek for fire and to wash, in reference to its use as a way to remove tints from glass.

Pyrolusite and romanechite are among the most common manganese minerals. Pyrolusite occurs associated with manganite, hollandite, hausmannite, braunite, chalcophanite, goethite and hematite under oxidizing conditions in hydrothermal deposits. It also occurs in bogs and often results from alteration of manganite.

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; indeed, chlorine gas itself was first described by Karl Scheele in 1774 from the reaction products of pyrolusite and hydrochloric acid. Natural pyrolusite has been used in batteries, but high-quality batteries require synthetic products. Pyrolusite is also used to prepare 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 (making it classically useful to glassmakers as a decolorizer). 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.