Fe 2 O 3 has two homogeneous multi-image variants: α-Fe 2 O 3 and γ-Fe 2 O 3 . The former trigonal system, with corundum-type structure, stable in nature, called hematite. The latter is an equiaxed crystal system with a spinel structure and is in a metastable state in nature, called maghemite. The trigonal hematite is described below. [Chemical composition] often contains Ti, Al, Mn, Fe 3+ , Cu and a small amount of Ca, Co-like mixed image. Sometimes, a mixture of TiO 2 , SiO 2 , Al 2 O 3 or the like is contained. [Crystal Structure] Trigonal System; [Form] The single crystal is often plate-shaped, and is mainly formed by a plate surface (parallel double-sided) and a rhombohedron (Fig. Y-7). The aggregates are diverse in form: crystalline, scaly or massive; cryptic crystals are scorpion, kidney, powder and earth. The names of some form of hematite and other characteristics, but also the following: a sheet having metallic luster by the assembly, said hematite (FIG Y-8); Brachymystax a sheet with metallic luster by the assembly, said mica Hematite; a scorpion or kidney-like hematite or kidney-like hematite; powdered hematite is called iron meteorite. The relationship between the morphological characteristics of hematite and its forming conditions is that hematite, which is generally formed by hydrothermal action, can be in the form of plates, flakes or rhombohedrons; mica hematite is a product of sedimentary metamorphism; And renal hematite is a product of sedimentation. Figure Y-7 Crystal aggregate of hematite Figure Y-8 Mirror iron ore crystal aggregate [Physical properties] The crystalline hematite is iron black to steel gray, cryptocrystalline scorpion, kidney and powder are dark red; streaks cherry red; metallic luster (mirror iron, mica hematite Mineral) to semi-metallic luster, or earthy luster; opaque. No clerk. The hardness is 5.5 to 6, and the soil is significantly reduced. The relative density is 5.0 to 5.3. Crisp. Mirror iron ore often has strong magnetic properties due to the inclusion of fine inclusions of magnetite. [genesis and occurrence] Hematite is one of the iron minerals widely distributed in nature. It can be formed in various geological processes, but mainly hydrothermal action, sedimentation and sedimentary metamorphism. [Identification characteristics] Cherry red streak is the most important feature for identifying hematite. In addition, morphology and non-magnetic (except for speclite) can be distinguished from magnetite. [Main use] It is the most important ore mineral for iron extraction. When the content of Ti and Co in the composition is high, it can be comprehensively utilized.
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a 0 =0.503 nm, c 0 =1.376 nm; Z=6. The crystal structure is corundum type. 
Hematite
α-Fe 2 O 3