Magnesite is a magnesium carbonate mineral, and it is the main source of magnesium. Magnesium-containing solutions act on calcite and turn calcite into magnesite, so magnesite belongs to calcite group. Magnesium rich rocks also change into magnesite. Magnesite often contains iron, which is the result of substitution of iron or manganese for magnesium. Magnesite is white or gray, with glass luster. Iron containing magnesite will appear yellow to brown. If the crystal is granular, if it does not show crystals, it is massive. Magnesite can also be used as refractory material and magnesium compound instead of magnesium.