Dolomite -CaMg (CO3)2 (m.p. 4800oF/2650o C) is used as an inexpensive source of Magnesia in glazes. It is a double Carbonate of Calcium and Magnesium, and a true Dolomite is typically 56% CaCO3 and 44% MgCO3 by weight. It can be used in clay bodies to promote longer and lower firing ranges (below cone 9), and used as a high temperature flux to promote crystal formations.