Description | This white mineral is magnesite, MgCO3 (magnesium carbonate). Magnesite forms commonly by alteration of magnesium-rich rocks during low grade metamorphism. It is closely related to calcite (but contains magnesium instead of calcium) and the two minerals would be hard to tell apart, except that calcite reacts vigorously to dilute hydrochloric acid. Magnesite may sometimes be confused with dolomite, another carbonate mineral. This specimen is from Gabbs, Nevada, where magnesite was mined during World War II. It is 9 cm across. |