Magnesit

Magnesite is a magnesium carbonate mineral with the chemical formula MgCO3. It forms in metamorphic and sedimentary environments, often as nodules or veins within carbonate rocks such as dolostone and limestone. It can develop through alteration of magnesium-rich rocks or by diagenetic replacement and also occurs in hydrothermal veins. Worldwide deposits are found in various geological settings, sometimes alongside dolomite, calcite, quartz, serpentine, and talc.

In terms of properties, magnesite crystals are typically rhombohedral and may appear white to colorless, or pale gray; impurities can give brown to yellow hues. The mineral has a vitreous to pearly luster, a Mohs hardness of about 3.5 to 4, and a specific gravity near 2.96. It readily effervesces with dilute acids due to its carbonate content and exhibits rhombohedral cleavage.

Industrial and other uses are dominated by its role as a source of magnesium oxide (MgO) after calcination: MgCO3 → MgO + CO2. MgO is used as a refractory material, a cement additive, and in steelmaking desulfurization, as well as a filler in ceramics and various industrial applications. Magnesite is also used as a petty gemstone or carved ornament in jewelry and decorative objects, particularly in white or pale specimens.

See also: List of minerals, Magnesium oxide, Dolomite.