What are the important types of iron ore

There are many kinds of iron minerals. At present, there are more than 300 kinds of iron minerals and iron-containing minerals, of which more than 170 are common. However, under current technical conditions, the main products with industrial use value are magnetite, hematite, maghemite, ilmenite, limonite and siderite. 1. Magnetite FeO 31.03%, Fe2O3 68.97% or Fe 72.2%, O 27.6%, equiaxed crystal system. Single crystals are often octahedrons, rarely rhombic dodecahedrons. On the surface of the rhombus dodecahedron, stripes often appear in the direction of the long diagonal. The aggregates are mostly dense blocks and granular. The color is iron black, the streaks are black, semi-metallic luster, and opaque. The hardness is 5.5~6.5. The proportion is 4.9~5.2. With strong magnetism. In magnetite, there is often a considerable amount of Ti4+ that replaces Fe3+ with isomorphism, and it is accompanied by Mg2+ and V3+ to replace Fe2+ and Fe3+ accordingly, thus forming some mineral subspecies, namely: (1) Titanium magnetite Fe2+(2) +x)Fe3+(2-2x)TixO4(0<x<1), containing TiO212%~16%. At room temperature, titanium is separated into plate-like and column-like ilmenite and cloth-like ilmenite spar. (2) Vanadium magnetite FeV2O4 or Fe2+(Fe3+V)O4, containing V2O5 sometimes as high as 68.41%~72.04%. (3) Vanadium-titanium magnetite is a solid solution product of the above two minerals with more complex compositions. (4) Chrome magnetite contains Cr2O3 up to several percent. (5) Magnesium magnetite contains MgO up to 6.01%. Magnetite is the main iron ore in magmatic iron deposits, contact metasomatic-hydrothermal iron deposits, sedimentary metamorphic iron deposits, and a series of iron deposits related to volcanism. In addition, it is also common in placer deposits. Magnetite can become hematite (false hematite and limonite) after oxidation, but it can still maintain its original crystal form. 2. There are known two kinds of homogeneous and polymorphic variants of Fe2O3 in nature in hematite, namely α-Fe2O3 and γ-Fe2O3. The former is stable under natural conditions and is called hematite; the latter is not as stable as α-Fe2O3 under natural conditions and is in a metastable state, and is called maghemite. Hematite: Fe 69.94%, O 30. 06%, often containing similar mixed substances Ti, Al, Mn, Fe2+, Ca, Mg and a small amount of Ga and Co. Trigonal crystal system, intact crystals are rare. The crystalline hematite is steel gray and cryptocrystalline; the earthy hematite is red. The streaks are cherry red or fresh pork liver color. Metal to semi-metallic luster. Sometimes the gloss is dim. Hardness 5~6. The proportion is 5~5.3. The aggregates of hematite have various forms, forming some mineral subspecies, namely: (1) Specularite is an aggregate of rosette or flaky hematite with metallic luster. (2) Mica hematite is a crystalline fine scaly hematite with metallic luster. (3) Oolitic or shen-shaped hematite in the form of oolitic or shen-shaped hematite. Hematite is one of the iron minerals widely distributed in nature. It can be formed in various geological processes, but is mainly hydrothermal, sedimentary and regional metamorphism. In the oxidation zone, hematite can be formed by dehydration of limonite, lepidocrocite and goethite. But it can also be turned into goethite and water hematite. Under reducing conditions, hematite can be transformed into magnetite, which is called pseudomagnetite. 3. Maghemite γ-Fe2O3, its chemical composition often contains mixed substances such as Mg, Ti and Mn. Equiaxed crystal system, pentagonal tritetrahedral crystals, mostly granular aggregates, dense masses, often with the illusion of magnetite. The color and streaks are both brown, hardness 5, specific gravity 4.88, and strong magnetism. Maghemite is mainly formed by secondary changes of magnetite under oxidizing conditions. Fe2+ ​​in magnetite is completely replaced by Fe3+ (3Fe2+→2Fe3+), so there are vacancies in the eight-sided position occupied by 1/3Fe2+. In addition, maghemite can be formed by the loss of water from lepidocrocite, and it can also be formed by the organic action of iron oxides. 4. Limonite is not actually a mineral species, but a mixture of goethite, lepidocrocite, hydrogoethite, hydrolepidocrocite, hydrous silicon oxide, argillaceous, etc. The chemical composition changes greatly, and the water content also changes greatly. (1) Goethite α-FeO(OH), containing 62.9% Fe. Those with indefinite amount of adsorbed water are called water goethite HFeO2·NH2O. The orthorhombic crystal system has the shape of needle, column, thin plate or scaly. It is usually bean-shaped, shen-shaped or stalactite-shaped. Cut the face into parallel or radial fibrous structures. Sometimes it is dense, lumpy, earthy, or oolitic. The color is reddish brown, dark brown to black brown. The weathered powdered, ocher-like limonite is yellowish brown. Goethite streaks are reddish brown, hardness 5~5.5, specific gravity 4~4. 3. The limonite streaks are generally light brown or yellowish brown, with a hardness of 1 to 4 and a specific gravity of 3.3 to 4. (2) Lepidocrocite γ-FeO(OH), containing 62.9% Fe. Those that contain an indefinite amount of adsorbed water are called hydroplecite FeO(OH)·NH2O. Orthogonal crystal system. Common scaly or fibrous aggregates. The color is dark red to black red. The streaks are orange or brick red. Hardness 4~5, specific gravity 4.01~4.1. 5. Ilmenite FeTiO3, Fe 36.8%, Ti 36.6%, O 31.6%. Trigonal crystal system. Rhombohedral crystals. It is often irregularly granular, scaly or thick. Above 950℃, ilmenite and hematite form a complete isomorphism. When the temperature is lowered, melting occurs, so ilmenite often contains fine scaly hematite inclusions. The color of ilmenite is iron black or steel gray. The streaks are steel gray or black. When containing hematite inclusions, it is brown or brownish red streaks. Metal-semi-metallic luster. Opaque and uncleavable. Hardness 5~6.5, specific gravity 4~5. Weakly magnetic. Ilmenite mainly occurs in ultrabasic rocks, basic rocks, alkaline rocks, acid rocks and metamorphic rocks. In the Panzhihua vanadium-titanium magnetite deposit in China, ilmenite is distributed between mineral particles such as titanomagnetite in granular or flake form, or oriented lamellae along the cracking surface of titanomagnetite. 6. Siderite FeCO3, FeO 62.01%, CO2 37.99%, often containing Mg and Mn. Trigonal crystal system. Rhombohedrons are common, and the crystal faces are often curved. The aggregates are coarse-grained to fine-grained. There are also tuberculous, grape-shaped, and earthy ones. Yellow, light brown yellow (dark brown after weathering), glass luster. The hardness is 3.5 to 4.5, and the specific gravity is about 3.96, which varies with the content of Mg and Mn. 6%. Trigonal crystal system. Rhombohedral crystals. It is often irregularly granular, scaly or thick. Above 950℃, ilmenite and hematite form a complete isomorphism. When the temperature is lowered, melting occurs, so ilmenite often contains fine scaly hematite inclusions. The color of ilmenite is iron black or steel gray. The streaks are steel gray or black. When containing hematite inclusions, it is brown or brownish red streaks. Metal-semi-metallic luster. Opaque and uncleavable. Hardness 5~6.5, specific gravity 4~5. Weakly magnetic. Ilmenite mainly occurs in ultrabasic rocks, basic rocks, alkaline rocks, acid rocks and metamorphic rocks. In the Panzhihua vanadium-titanium magnetite deposit in China, ilmenite is distributed between mineral particles such as titanomagnetite in granular or flake form, or oriented lamellae along the cracking surface of titanomagnetite. 6. Siderite FeCO3, FeO 62.01%, CO2 37.99%, often containing Mg and Mn. Trigonal crystal system. Rhombohedrons are common, and the crystal faces are often curved. The aggregates are coarse-grained to fine-grained. There are also tuberculous, grape-shaped, and earthy ones. Yellow, light brown yellow (dark brown after weathering), glass luster. The hardness is 3.5 to 4.5, and the specific gravity is about 3.96, which varies with the content of Mg and Mn. 6%. Trigonal crystal system. Rhombohedral crystals. It is often irregularly granular, scaly or thick. Above 950℃, ilmenite and hematite form a complete isomorphism. When the temperature is lowered, melting occurs, so ilmenite often contains fine scaly hematite inclusions. The color of ilmenite is iron black or steel gray. The streaks are steel gray or black. When containing hematite inclusions, it is brown or brownish red streaks. Metal-semi-metallic luster. Opaque and uncleavable. Hardness 5~6.5, specific gravity 4~5. Weakly magnetic. Ilmenite mainly occurs in ultrabasic rocks, basic rocks, alkaline rocks, acid rocks and metamorphic rocks. In the Panzhihua vanadium-titanium magnetite deposit in China, ilmenite is distributed between mineral particles such as titanomagnetite in granular or flake form, or oriented lamellae along the cracking surface of titanomagnetite. 6. Siderite FeCO3, FeO 62.01%, CO2 37.99%, often containing Mg and Mn. Trigonal crystal system. Rhombohedrons are common, and the crystal faces are often curved. The aggregates are coarse-grained to fine-grained. There are also tuberculous, grape-shaped, and earthy ones. Yellow, light brown yellow (dark brown after weathering), glass luster. The hardness is 3.5 to 4.5, and the specific gravity is about 3.96, which varies with the content of Mg and Mn.

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