Magnesite - MgCO₃

Habit: Colorless, white, pale yellow, pale brown, faintly pink or lilac rose. Uncommon as crystals; typically earthy, chalky, porcelaneous, fibrous, coarse to fine granular, compact or massive. Vitreous luster; transparent to translucent. White streak.

Environment: A primary mineral in igneous or sedimentary rocks, formed by metamorphism or alteration of serpentine and peridotite. Uncommon in marine evaporites and hydrothermal veins and rare in carbonatites.

Etymology: Named for the magnesium in its composition. An ore of magnesium commonly used as a refractory material, magnesite has a very high melting point, making it ideal for lining furnaces. It is also used as a catalyst and filler in the production of synthetic rubber and in the preparation of magnesium chemicals for fertilizers.