Pyrolusite

In short

Pyrolusite is manganese dioxide (MnO₂), one of the commonest manganese oxide minerals. It forms earthy masses between steel-grey and black that stain the fingers, or rarely needle-like crystals. Its name comes from the Greek words for “fire” and “to wash”, because it was used to remove the colour from glass. Its main use is as manganese ore: 85–90 percent of manganese demand goes into steelmaking. In Türkiye pyrolusite occurs in many places, but most of the deposits are small and low in grade.

Photos

How to recognise it

1. 1

   Steel-grey, iron-grey or black; the crystals are metallic, while the earthy mass is dull and shades into bluish black. The streak is black or bluish black, and it stains fingers and paper.

2. 2

   Hardness varies: crystals are 6–6.5 on the Mohs scale, but earthy masses are as soft as 2 and crumble in the hand. The density is about 4.4–5 g/cm³, so it feels heavy.

3. 3

   Crystals are rare and form needle-like, fibrous bundles; it is more often found as botryoidal, kidney-shaped or powdery masses. The cleavage is perfect on {110}.

4. 4

   Other manganese oxides (such as psilomelane, manganite, braunite and hausmannite) look very much like it; telling them apart for sure takes X-ray diffraction (XRD) or a microscope. The black branching patterns on rock surfaces are often called “pyrolusite”, but that is mostly wrong.

Myths and misconceptions

• MythThe black fern-like or moss-like patterns on rock surfaces are fossil plants.

  FactThey are not fossils but mineral patterns called dendrites. As water rich in manganese and iron moves along cracks and bedding planes in the rock, black manganese oxides grow in branching shapes; there is no trace of a living thing in them. That is why they are called “pseudofossils”.

• MythThese black tree-like patterns are pyrolusite.

  FactAlthough many sources say so, careful analyses of numerous examples of these dendrites have found that none of them are pyrolusite (Wikipedia). They are usually other manganese oxides and hydroxides such as birnessite, romanèchite, todorokite, cryptomelane, hollandite and coronadite.

• MythThe manganese dioxide in batteries is pyrolusite taken straight from the mine.

  FactNatural pyrolusite has been used in batteries, but high-quality batteries need synthetic manganese dioxide (Wikipedia).

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Where is it found?

• Horní Blatná (Platten), Karlovy Vary Region, Czechia · Known localityThe Handbook of Mineralogy cites good pyrolusite crystals from Horní Blatná; its chemical analysis (98.7 percent MnO₂) is of a sample from here. The point is the approximate position of the town.
• Ilmenau area (Elgersburg, Öhrenstock), Thuringia, Germany · Historic sourceThe Handbook of Mineralogy lists Elgersburg, Friedrichroda and Öhrenstock near Ilmenau in Thuringia among the well-studied pyrolusite localities. The point is the position of the town of Ilmenau.
• Eibenstock, Saxony, Germany · Historic sourceOne of the German localities the Handbook of Mineralogy gives for pyrolusite. The point is the position of the town of Eibenstock.
• Ironwood, Gogebic County, Michigan, USA · Major depositThe Handbook of Mineralogy lists Ironwood (Michigan) among the large pyrolusite deposits of the USA. The point is the position of the city of Ironwood.
• Leadville, Lake County, Colorado, USA · Known localityOne of the US localities the Handbook of Mineralogy gives for pyrolusite. The point is the position of the city of Leadville.
• Thrace manganese belt (Çatalca–Kırklareli: Çatalca, Binkılıç, Çakıllı), Türkiye · Major depositAccording to Ateşok, Türkiye's largest and most economic manganese deposits, of sedimentary type, lie in this belt running from Çatalca to Kırklareli; the ore minerals are mainly pyrolusite and psilomelane, with manganite in places. The point is roughly the middle of the belt. The data are old (1970s).
• Tavas (Ulukent), Denizli, Türkiye · Major depositAccording to Yüce and colleagues (1990s), the Denizli–Tavas deposit, with a reserve of about 4 million tons, was the biggest working mine in Türkiye, producing 25,000 tons of ore a year; the ore holds about 30 percent braunite and 24 percent rhodochrosite by weight, while pyrolusite and psilomelane make up only about 7 percent and formed mostly as fracture fillings from the alteration of braunite. The point is the position of the town of Tavas.
• Kınık village area, Sındırgı, Balıkesir, Türkiye · Known localityYüce and colleagues report that the ore of the manganese occurrence here consists mainly of pyrolusite, psilomelane and manganite (about 30 percent Mn); a 46 percent Mn concentrate was made by physical methods. The point is the position of the town of Sındırgı.
• İliç, Erzincan, Türkiye · Known localityAccording to Ateşok, in the İliç deposit, of hydrothermal origin, the ore minerals are mainly psilomelane and pyrolusite; the average Mn content is 43–45 percent and about 100,000 tons of visible reserves were found. The data are old. The point is the position of the town of İliç.
• Haymana, Ankara, Türkiye · Known localityAccording to Ateşok, in the three pits at Haymana the ore minerals are generally pyrolusite and hausmannite; the Mn grade is about 47 percent and the visible and probable reserve about 215,000 tons. The data are old. The point is the position of the town of Haymana.

Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →