Magnesite (MgCO₃) is the magnesium end-member of the calcite-group carbonates. It forms by hydrothermal alteration of ultramafic rocks and as primary precipitate in evaporite basins. Brumado (Brazil) supplies gem-quality transparent magnesite; massive cryptocrystalline “porcelain magnesite” from Liaoning (China) is the dominant industrial source for refractories.
Key Facts
- Mohs hardness 4–4.5.
- Trigonal; isostructural with calcite and dolomite.
- Pure white or color from impurities (yellow Fe, pink Mn).
- Major source of magnesium oxide for refractory bricks and Mg metal.
- Forms continuous series with siderite (Fe) and rhodochrosite (Mn).
Notable Localities
Brumado (Bahia, Brazil) yields gem-grade transparent rhombohedrons. Liaoning (China) hosts massive cryptocrystalline industrial deposits.
Found at these Localities
- Eastern Brazilian Pegmatite Province (巴西东部伟晶岩省)
