(redirected from marcasites)
Also found in: Dictionary.


(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
..... Click the link for more information.
. 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.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
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 It might be outdated or ideologically biased.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
References in periodicals archive ?
Black crystals of cronstedtite with triangular cross-section, displaying only {20[bar.2]1} and {0001} faces, as well as compact masses of cronstedtite, were once found on hisingerite, marcasite, pyrite, siderite and rhodochrosite.
Denning, consists of a 3-cm marcasite pseudomorph after pyrrhotite intergrown with quartz, the surface of which is encrusted with microcrystals of colorless wavellite, pinkish sphalerite, orange greenockite and sparse, porcelaneous, white spheres of faustite.
It has been found commonly as tabular to platy, brilliantly metallic crystals and thin, black, flexible laminae resembling graphite, usually in association with marcasite and wurtzite.
Specimens with minute red greenockite crystals (0.1 mm) sprinkled on wavellite, quartz, cassiterite or marcasite are now widely distributed in micromount collections.
Greenockite at Llallagua is widespread in small quantities, in all the veins but especially in the richer ore shoots where it coats marcasite and wavellite.
Marcasite crystals are plentiful but small, rarely more than about 1 mm in size.
Pyrrhotite was widespread as hexagonal, tabular to barrel-shaped prismatic crystals, but almost all of the original pyrrhotite has been replaced by pyrite and marcasite. Pseudomorphic crystals can reach 15 cm, and some are covered by a wavellite crust.
Sulfur is found as minute yellow crystals, usually with bismuthinite or marcasite. According to Bandy (1944), some of this sulfur may be of primary origin, though Gordon (1944) believed it to be an alteration product of bismuthinite.
In one particularly large fissure in the footwall fine crystals in spherical aggregates were found perched on quartz, wavellite, marcasite and other minerals, associated with minor paravauxite.