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 ?
The XRD spectra, not shown, allowed the Fe oxides goethite, hematite and maghemite to be identified.
The [Al.sup.3+] substitution values for hematite, 0.05-0.08mol [mol.sup.-1], fell in the central range.
La complementariedad de diferentes analisis ha hecho posible asimismo determinar la cadena operativa de obtencion y posible uso de la hematites en el Neolitico antiguo de Cova de l'Or (Garcia Borja et al., 2004; Garcia Borja et al., 2006; Domingo et al., 2012; Roldan et al., 2008).
El objeto de la investigacion es un reducido lote de hematites y ocres con estigmas de uso, recuperado en la cueva de Zatoya (Abaurrea Alta, Navarra), yacimiento clave, de obligada referencia, para el conocimiento de la evolucion cultural de grupos de cazadores-recolectores desde finales del Tardiglaciar a mediados del Holoceno en este territorio de montana del prepirineo noroccidental (Barandiaran y Cava, 1989).
Wells MA, Gilkes RJ, Fitzpatrick RW (2001) Properties and acid dissolution of metal-substituted hematites. Clays' and Clay Minerals 49, 60-72.
The substitution of aluminium (Al) in soil goethitc and hematite has been well established; however, the association of trace elements has received only limited attention (Fontes and Weed 1991; da Motta and Kampf 1992; Singh and Gilkes 1992; Trakoonyingcharoen et al.
Finally, the as-formed hematite nanoparticles would be further coarsened by an oriented-assembling mode in order to reduce the surface energy of [alpha]-[Fe.sub.2][O.sub.3] particles which were polar crystals and tended to spontaneously assemble [15,16].
A qualitative analysis of the X-ray pattern was done by using data from JCPDS (1980) cards 24-0072 (hematite) and 19-926 (magnetite) (Table 2).
They contain broadly equal quantities of quartz, kaolinite, and goethite, and lesser amounts of hematite (samples are grouped in cluster D).
Clay contents of hematite (Hm) and goethite (Gt) were semiquantified from the ratio Hm/Hm + Gt and the difference [Fe.sub.d]--[Fe.sub.o].
All diffraction peaks could be indexed to hematite with a hexagonal corundum-type crystal structure of space group R[bar.3]c and are attributed to the HNM particles.
Most collectors (even in Europe) who number hematite iron roses among their favorites tend to be rather vague about just where the best examples come from, and their specimens' labels are often unhelpful.