One of the primitive earths, having a metallic base called magnesium. It is a soft white powder; of specific gravity 2.3. It renders the syrup of violets, and the infusion of red cabbage, green; and reddens turmeric. It is infusible, except by the oxy-hydrogen blow-pipe. It has scarcely any taste, and no smell; is nearly insoluble in water, but absorbs that liquid with the production of heat. Its chief use is in medicine.