| Pyrolusite | |
|---|---|
 | |
| General | |
| Category | Oxide minerals |
| Formula | MnO2 |
| IMA symbol | Pyl[1] |
| 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 | Irregular/Uneven |
| Tenacity | 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 | [2][3][4][5] |
| Major varieties | |
| Polianite | pseudomorphic aftermanganite[6] |
Pyrolusite is amineral consisting essentially ofmanganese dioxide (MnO2) and is important as anore of manganese.[7] It is a black,amorphous appearing mineral, often with a granular, fibrous, or columnar structure, sometimes formingreniform crusts. It has a metallicluster, a black or bluish-black streak, and readily soils the fingers. Thespecific gravity is about 4.8. Its name is from the Greek forfire and towash, in reference to its use as a way to remove tints from glass.[5]
Pyrolusite andromanechite are among the most common manganese minerals. Pyrolusite occurs associated withmanganite,hollandite,hausmannite,braunite,cryptomelane, chalcophanite,goethite, andhematite underoxidizing conditions inhydrothermal deposits. It also occurs inbogs and often results from alteration of manganite.[5] it can also occur alongsiderhodonite, which is generally pink.
The metal is obtained by reduction of the oxide withsodium,magnesium,aluminium, or byelectrolysis. Pyrolusite is extensively used for the manufacture ofspiegeleisen andferromanganese and of various alloys such as manganese-bronze. As an oxidizing agent it is used in the preparation ofchlorine; indeed, chlorine gas itself was first described byKarl Scheele in 1774 from the reaction products of pyrolusite andhydrochloric acid. Natural pyrolusite has been used in batteries, but high-quality batteries requiresynthetic products. Pyrolusite is also used to prepare disinfectants (permanganates) and for decolorizing glass. When mixed with molten glass it oxidizes the ferrousiron 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.
Black, manganese oxides with adendriticcrystal habit often found on fracture or rock surfaces are often assumed to be pyrolusite although careful analyses of numerous examples of these dendrites has shown that none of them are, in fact, pyrolusite. Instead, they are other forms of manganese oxide.[8][9]
Some of the most famous early cave paintings in Europe were executed by means of manganese dioxide. Blocks of pyrolusite are found often atNeanderthal sites. It may have been kept as a pigment forcave paintings, but it has also been suggested that it was powdered and mixed withtinder fungus for lighting fires.[10] Manganese dioxide, in the form ofumber, was one of the earliest natural substances used by human ancestors. It was used as apigment at least from theMiddle Paleolithic. It may have been also used by theNeanderthals in fire-making.[11]
The ancient Greeks had a term μάγνης or Μάγνης λίθος ("Magnes lithos") meaning stone of the area called Μαγνησία (Magnesia), referring toMagnesia in Thessaly or to areas inAsia Minor with that name. Two minerals are called μάγνης, namelylodestone and pyrolusite (manganese dioxide).(not to be confused with the current mineral called Lodestone, which does not contain Manganese. Lodestone is a naturally magnetized form of the iron mineral Magnetite. FeFe2O4)The term μαγνησία was used for manganese dioxide. In the sixteenth century it was called "manganesum". It also was called Alabandicus (from theAlabanda region of Asia Minor) and Braunstein. Eventually the name of the element manganese was derived from "manganesum", whereas "magnesia" came to mean the oxide of a different element,magnesium.[12]
Other manganese oxides:
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Pyrolusite".Encyclopædia Britannica. Vol. 22 (11th ed.). Cambridge University Press. p. 693.
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