Cryolite is a brittle, icy-looking red, brown, or black halide mineral, sodium-aluminum fluoride (Na3AlF6) found in pegmatite dikes (Greenland has the only large deposits). It occurs as crystals in the monoclinic system, occasionally the cubic system, sometimes as granular masses. The crystals are frequently twinned. Molten cryolite is used to dissolve bauxite ore in the electrolytic production of aluminum. Cryolite is also a source of aluminum salts and fluorides.