Psilomelane(redirected from Black hematite)
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Related to Black hematite: red hematite, specular hematite
a mineral, a complex hydrous manganese oxide. Its approximate chemical composition is given by the formulas
(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.