magnesite

Magnesite is a mineral with the chemical formula MgCO3. It is a magnesium carbonate mineral and an important ore for magnesium. Crystallizing in the trigonal system, magnesite commonly forms rhombohedral crystals or exists as massive, earthy to microcrystalline aggregates. Its color ranges from white to colorless, with impurities producing gray, yellow, or brown hues. The mineral has a vitreous to pearly luster and a white streak. It is named after the Magnesia region in Greece.

Formation and occurrence: Magnesite forms through low-temperature metamorphism and metasomatism of magnesium-rich limestones and dolostones, and by direct precipitation from magnesium-rich waters in sedimentary or hydrothermal environments. It is commonly found in veins and replacement bodies, often associated with talc, quartz, dolomite, and serpentine, and occurs in various geological settings, including ophiolites and ultramafic terrain.

Physical and chemical properties: Magnesite has a hardness of about 3.5 to 4 on the Mohs scale and a specific gravity near 3.0. It effervesces in dilute acids, releasing carbon dioxide. Upon heating, magnesite decomposes to magnesium oxide and carbon dioxide, with calcination producing a useful refractory material. It is relatively inert in water but dissolves in acids.

Uses and production: The principal industrial use of magnesite is as a source of magnesium oxide (MgO) after calcination, which yields magnesia used in refractory bricks, crucibles, and other high-temperature applications, as well as in steelmaking and cement kilns. Magnesium carbonate derived from magnesite is used as a filler in paints, plastics, and paper, and the oxide from magnesite serves as a feedstock for magnesium metal production in specialized processes. Magnesite deposits are distributed worldwide, with producing regions including China, Slovakia, Turkey, and Austria.