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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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.

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.
References in periodicals archive ?
The alteration mapping adds further evidence of IOCG style mineralization with intense chlorite and specular hematite alteration as important vectors to mineralization.
The surprising result was that the hematite remained magnetic up to a temperature of around 925 C (1,200 K) the temperature prevailing in the subducted slabs beneath the western part of Pacific Ocean at the Earths transition zone depth.
The Feo/Fed ratio range from 0.01 to 0.83 but was less than 0.10 in most cases, suggesting a prevalence of crystalline forms (goethite, hematite and maghemite); also, the contents in poorly crystalline oxides --ferrihydrite, mainly-- were comparatively low (SCHWERTMANN et al., 1982).
The mineral suspension (either chlorite or hematite) was prepared by adding 3.0 g of minerals to 40 ml of distilled water.
The mill scale originating in the steel production process consists of mainly three types of iron oxides: wustite FeO, magnetite [Fe.sub.3][O.sub.4], and hematite [Fe.sub.2][O.sub.3] [13].
The hematite characteristic reflections are: 24.182o, 33.205[degrees], 35.67[degrees], 39.341[degrees], 40.910[degrees], 50.533[degrees], 54.149[degrees], and 72.065[degrees] while the magnetite characteristic reflections are: 18.28[degrees], 30.08[degrees], 35.43[degrees], 37.071[degrees], 43.070[degrees], 53.43[degrees], 56.95[degrees], 62.546[degrees], 70.95[degrees], and 73.992[degrees], figure 2.
Hematite phase presents bands at 620, 540, and 470 [cm.sup.-1] and maghemite phase presents bands at 700, 660-630, 590, and 430 [cm.sup.-1], but the positions of the bands are sensitive to the particles size and shape [26, 27].
Hakro [8] reported the sediments of Bara Formation from Ranikot area are composed of quartz (low), hematite, potash feldspar, gypsum and goethite minerals.
The analytical work revealed that marble was used in combination with red sandstone for the characteristic representation of Mughal architecture instead of the black/ green schist and basalt used during earlier architectural periods for monumental ornamentation in Indian subcontinent (Chandra, 2003 and Awan, 2008).Investigations and analytical study of marble samples depictedmetamorphic recrystallization,so that the fret marble was found to be a coarse grained rock of interlocking carbonate crystals with few percent of quartz, hematite, limonite and mica.
Hematite and magnetite ore deposits are mostly found in the province of Northern Cape.