psilomelane

[‚sī·lō′me‚lān]

(mineralogy)

BaMn₉O₁₆(OH)₄ A massive, hard, black, botryoidal manganese oxide mineral mixture with a specific gravity ranging from 3.7 to 4.7.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Psilomelane

a mineral, a complex hydrous manganese oxide. Its approximate chemical composition is given by the formulas

BaMn²⁺Mn₉⁴⁺O₂₀.3H₂O

(Ba, Mn²⁺)₃(O, OH)₆Mn₈⁴⁺O₁₆

Psilomelane crystallizes in the monoclinic system. Its structure is formed by chains of the octahedral group MnO₆ with large channels, in which barium and molecules of water are positioned as in zeolite minerals. Ba ions in the channels can be replaced by ions of Ca, K, Pb, Zn, Co, Ni, Cu, U, and Sr; the Mn ions can be replaced by those of W, Fe, Al, and V. Psilomelane is opaque, and its color is black, steel gray, or brownish black. Its luster is submetallic; in fine-grained masses, it is dull. In massive form, the hardness on Mohs’ scale is 5–6; in finegrained masses, it is 1–3. The mineral’s density is 4,000–4,700 kg/m³.

Psilomelane occurs admixed with other oxides of manganese and iron in the form of smooth-surfaced, cryptocrystalline, or sinter aggregates. Soft, loosely aggregated substances that soil the fingers and possess a chemical composition similar to that of psilomelane are called wads. Psilomelane is of sedimentary or, less frequently, of hydrothermal origin. It also occurs in the zone of oxidation of oxide, silicate, and carbonate ores of manganese deposits. Psilomelane, together with other minerals that are oxides of manganese, is an important industrial ore in the smelting of ferromanganese. Psilomelane ores deficient in manganese are used for blending in the smelting of ordinary pig iron.

REFERENCE

Mineraly: Spravochnik, vol. 2, fasc. 3. Moscow, 1967.

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References in periodicals archive

Many nodules were once hollow and have since been filled with manganese minerals (primarily psilomelane and cryptomelane), the probable coloring agents for the agate.

Classic agate deposits: of Northern Mexico

Black, inammillary "psilomelane" was reported by both Weed (1912) and Pardee (1918) from vein outcrops on the north and southwestern sides of the district, where it formed as a product of the oxidation of rhodochrosite and especially rhodonite.

Butte, Montana: Minerals, mines, and history

Psilomelane, a mixture of manganese oxides, forms black dendrites on the faces of quartz and calcite crystals.

THE DODO DEPOSIT SUBPOLAR URALS, RUSSIA

At any rate, the 15 miniature to small cabinet-sized specimens here were all flat plates of a weathered granite with coatings of lustrous deep black mammillary psilomelane, this black layer sprinkled with sharp, gemmy, vividly deep yellow hexagonal prisms of mimetite, uniformly around 4 or 5 mm.

Rochester Mineralogical Symposium 1999

Black dendrites and thin films and crusts of "psilomelane" coat some of the silicified limestone drusy quartz in the area.

THE MEX-TEX MINE, BINGHAM, NEW MEXICO

Minerals found in these veins, where they outcrop, are quartz, tourmaline, rhodochrosite, calcite, pyrite, marcasite, galena, sphalerite, chalcopyrite, argentite, pyrolusite and psilomelane. These veins, which number over a dozen, vary from 30 cm to 2 meters thick.

The Raura-Huanzala Group

Second is the specimen of common but beautifully crystallized, acicular aragonite with black psilomelane shown in Figure 13.

Exchanging with Italian micromineral collectors