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(mär`kəsīt) or

white iron pyrites,

a mineral closely resembling and having the same chemical composition (FeS2) as pyritepyrite
or iron pyrites
, pale brass-yellow mineral, the bisulfide of iron, FeS2. It occurs most commonly in crystals (belonging to the isometric system and usually in the form of cubes and pyritohedrons) but is also found in massive, granular, and stalactite
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. It differs from pyrite in that it is paler in color, becomes darker upon oxidation, and crystallizes in the orthorhombic system. Twinned crystals resembling cockscombs (cockscomb pyrites) or spearheads (spear pyrites) are of common occurrence. The mineral occurs in marls, clays, and limestones in many parts of the world.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(also white iron pyrite), a mineral, a polymorphic variety of natural disulfide of iron, FeS2. Marcasite crystallizes in the orthorhombic system. The luster is metallic. Of bronze-yellow color, which changes to gray along the crystal surface, the mineral forms spear-shaped, often complex, twin crystals, comb-like and round concretions, or sooty black masses (melnikovitemarcasite). Marcasite has a hardness of 6-6.5 on Mohs’ scale and a density of 4,850- 4,900 kg/m3. It usually forms from natural subacid solutions at temperatures lower than the temperature at which pyrite forms. Marcasite is found in hydrothermal deposits in association with pyrite, pyrrhotite, and other sulfides; it often replaces pyrrhotite in the oxidized zone of sulfide deposits. Marcasite occurring in sedimentary rocks is particularly widespread in Carboniferous deposits containing sand and clay, where it forms irregular nodular and concretionary formations. The mineral is used in the preparation of sulfuric acid.


Mineraly; Spravochnik, vol. 1. Moscow, 1960.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


FeS2 A pale bronze-yellow to nearly white mineral, crystallizing in the orthorhombic system; hardness is 6-6.5 on Mohs scale, and specific gravity is 4.89.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


a metallic pale yellow mineral consisting of iron sulphide in orthorhombic crystalline form used in jewellery. Formula: FeS2
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005