hematite

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Related to hematites: red hematite

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 ?
With the exception of two samples (Ci and Ak3), Fe-oxide concentrates with high content of goethite also contained more Al (Tables 2 and 3), which is consistent with the greater Al substitution in goethite than hematite when they coexist.
3+] in the structures of goethite and hematite (Trolard et al.
The dissolution rate of goethite and hematite has been known to increase with increasing dissolution temperature, SSA and acid concentration (Chiarizia and Horwitz 1991; Cornell and Giovanoli 1993; Ruan and Gilkes 1995).
These values are smaller than expected for a stoichiometric hematite (around 51.
The non-magnetic sample was fitted with a 2-block hyperfine field distribution, one for hematite and other for goethite.
The relative subspectral area (Table 4) due to hematite increases from 60% to 86%.
Hematite preserved in cracks of etched quartz grains in the goethite cortex (Fig.
Features such as marked quartz etching, replacement of hematite by goethite, and high A1 substitution of goethite and hematite in these nodules are consistent with strong chemical weathering (Schwertmann and Carlson 1994).
In the present study, etched quartz grains were commonly observed in thin section, often filled by hematite or goethite (Fig.
For clays that did not have hematite, the goethite clay content was determined with the following equation:
Equations 2, 3, and 4 were derived considering that the respective unit cells of Al-substituted hematite and goethite are given by [Fe.
8, whereas kaolinite, gibbsite, hematite, and goethite reacted to a smaller extent.