Iron ore is mainly used in the steel industry. There are many kinds of iron minerals, and about 300 kinds of iron minerals and iron-containing minerals have been discovered, among which more than 170 are common. However, under the current technical conditions, the main industrial value is magnetite, hematite, maghemite, ilmenite, limonite and siderite.

Classification of magnetite

The chemical formula of magnetite is Fe3O4, and the theoretical iron content is 72.4%. This ore sometimes contains a composite ore of TiO2 and V2O5, which is called titanomagnetite or strontium titanomagnetite.

It is rarely encountered in natural pure magnetite ore, and some of the magnetite is often oxidized into semi-artificial hematite and imaginary hematite due to surface oxidation. The so-called imaginary hematite is the oxidation of magnetite (Fe3O4) to hematite (Fe2O3), but it still retains the shape of the original magnetite, so it is called imaginary hematite.

Magnetite has strong magnetism, crystals are often octahedral, and a few are rhombohedral dodecahedrons. The aggregates are often dense blocks, the color streaks are iron black, semi-metallic luster, relative density 4.9 ~ 5.2, hardness 5.5 ~ 6, no cleavage, gangue is mainly quartz and silicate, poor reduction, generally Harmful impurities are higher in sulfur and phosphorus.

Magnetite is widely distributed and has many causes. Kiruna, Sweden is a typical magma deposit. The Laco iron ore mine in Chile is formed directly from the pulp associated with volcanism. The iron ore formed by contact with metamorphism can be exemplified by China Daye Iron Mine. The iron ore formed by the metamorphism of the deposited iron-bearing strata (such as the iron ore in the Anshan area of China) is dominated by magnetite and hematite. It is large in scale but low in grade and is the most important in the world. Source of iron ore. The former Soviet Union, North America, Brazil, and Australia all have such large iron ore.