Bauxite Composition, Crystallization & Structure

    Composition. A12O (OH)4 or A12O3. 2H2O = Alumina 73.9, water 26.1. Often impure.

    Crystallization. Noncrystalline.

    Structure. In round concretionary grains; also massive, earthy, claylike.

    Physical Properties. G. = 2-2.55.  Dull to earthy luster.  Color white, gray, yellow, red.

    Test. infusible. Insoluble. Assumes a blue color when moistened with cobalt nitrate and then ignited (aluminum). Gives water in C.T.

    Occurrence. A mineral of secondary origin, commonly produced under tropical climatic conditions by the prolonged weathering of aluminum-bearing rocks. Also at times derived from the weathering of clay-bearing limestones. It has apparently originates as a colloidal precipitate. It may occur in place as a direct derivative of the original rock or it m ay have been transported and deposited in a sedimentary formation. In the tropics, deposits, known as laterites, consisting largely of aluminum and ferric oxides are found in t the residual soils. These vary widely in composition and purity but may at time become valuable as sources of aluminum and iron. Occurs over a large area in the south of France an important district being at Baux, near Arles, France. In the United States the chief deposits are found in Georgia, Alabama and Arkansas.

    Use, as an ore of aluminum, in the manufacture of aluminum salts; artificial abrasives and bauxite brick.