hematite

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hematite

(hĕm`ətīt), mineral, an oxide of iron, Fe2O3, containing about 70% metal, occurring in nature in red to reddish-brown earthy masses and in steel-gray to black crystalline forms. Hematite that has a metallic luster is called specular hematite, or specular iron. The red powdered hematite is used as a pigment (ocherocher
, mixture of varying proportions of iron oxide and clay, used as a pigment. It occurs naturally as yellow ocher (yellow or yellow-brown in color), the iron oxide being limonite, or as red ocher, the iron oxide being hematite.
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) and as rouge in polishing. Hematite is the most important ore of iron. Extensive and richly productive deposits occur in the Lake Superior region (Michigan, Minnesota, and Wisconsin) and the Birmingham district (Alabama). The mineral is widely distributed throughout the world and is responsible for the red coloration of many sedimentary rocks. See limonitelimonite
or brown hematite
, yellowish to dark brown mineral, a hydrated oxide of iron, FeO(OH)·nH2O, occurring commonly in deposits of secondary origin, i.e., those formed by the alteration of minerals containing iron.
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.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Hematite

 

a widely distributed ferrous mineral, Fe203, containing up to 70 percent iron. Hematite is crystallized in a trigonal system. Its crystals are steel gray with a semimetallic shine. Depending on the mineral aggregate structures and the crystallic concretion shapes, a distinction is made among (1) hematite iron glance (macrocrystalline concretions); (2) ferrous mica (flaky aggregates); (3) ferrous rosette (crystal concretions reminiscent of corollas of dog rose); (4) red ironstone (dense red microcrystallic units); (5) kidney ore (red dense reniform conglomerations); and (6) martite (dense or porous ore formations). On the mineralogical scale, the hardness is 5.5-6; the density, 5,260 kg per cu m. The powder is cherry red in color. The melting point is 1594° C.

Together with magnetite, geothite, and quartz, hematite is formed in deposits of different genetic types and in various rocks, when the oxidizing potential of the medium is sufficiently high. Hematite ores are ferrous ores of great importance, being used for smelting cast iron and steel. Iron content in solid hematite ores fluctuates from 50 percent to 65 percent. The largest deposits are connected with the oldest Precambrian ferriferous quartzites (jaspilites).

In the USSR the Krivoi Rog hematite ore deposit (in the Ukrainian SSR), the Kursk Magnetic Anomaly, and the Urals and Siberian deposits are well known. The biggest deposits abroad are situated near Lake Superior, Birmingham, and elsewhere in the USA; in the state of Minas Gerais in Brazil; and in Canada (Labrador), India (states of Bihar, Orissa, and Madhya Pradesh), and several countries of Africa.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

hematite

[′hē·mə‚tīt]
(mineralogy)
Fe2O3 An iron mineral crystallizing in the rhombohedral system; the most important ore of iron, it is dimorphous with maghemite, occurs in black metallic-looking crystals, in reniform masses or fibrous aggregates, or in reddish earthy forms. Also known as bloodstone; red hematite; red iron ore; red ocher; rhombohedral iron ore.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The peaks corresponding to the main features of haematite are also indicated.
An extreme learning machine based on the improved particle swarm optimization (IPSO-ELM) was used to process the spectral data of haematite to obtain a model for detecting the magnetic properties of haematite.
Haematite is a very hard stone, whereas red ochre is finely ground powder, or paste.
The haematite and goethite occurrences are interpreted to result from alteration and enrichment of the magnetite-bearing BIF, particularly in areas of complex folding.
The phenocrysts are alkali feldspar (Or60-65) [+ or -] clinopyroxene (Wo46-49Fs14-20) [+ or -] plagioclase (An14-16), pseudomorphosed leucite, amphibole, and biotite in a hypocrystalline to glassy groundmass containing microlites of alkali feldspar, biotite, and clinopyroxene [+ or -] biotite [+ or -] amphibole [+ or -] magnetite [+ or -] Ti-andradite [+ or -] haematite.
Furthermore clear, localised, well-defined, high magnetic anomalies could be observed around the western and west-central portions of the aeromagnetic maps of the study area (Figures 2 and 3) Total magnetic intensity values in the aforementioned areas varied from 7960nT to 8020nT, whereas residual magnetic intensity values ranged from 160nT to 220nT Iron ore is being mined by unskilled miners about 4km north of the town of Nasarawa Eggon; it could thus be inferred that the localised and well-defined high magnetic anomalies may have been associated with the presence of iron ore (having high magnetite to haematite ratio) or other metal-liferous mineral deposits within the basement rocks in the area.
The Red Hills Prospect occurs at the western end of a 60km long by 3km wide structural and stratigraphic corridor within which the sedimentary rocks show intense and widespread haematite and chlorite alteration, with local large airborne uranium anomalies.
Dolomite (0-5.6%) and haematite (0-2.3%) were also detected in several oil shale samples.
Iron ore is produced mainly after costly explorations, but sometimes iron ore surfaces from underground in a volcanic and hydrothermal process under which volcanic materials are split into elements like pegmatite, magnetic, haematite, limotite.
The Thermal Emission Spectrometer aboard MGS mapped surface deposits of haematite, a mineral formed in liquid water, thus offering landing targets for the Opportunity rover; its magnetometer mapped crustal magnetisation resulting from ancient dynamo action.
The most widely used lamellar pigment for anticorrosive barrier coatings is micaceous iron oxide (MIO), which essentially is a type of haematite ([Fe.sub.2][O.sub.3]).