The Encyclopedia Americana (1920)/Bauxite

BAUXITE, or BEAUXITE, bo'zīt (from Baux, or Beaux, near Arles, France, where it occurs), a native, hydrated oxide of aluminum, having the formula Al₂O₃2H₂O. It has a specific gravity of about 2.5, and its hardness ranges from 1 to 3. It occurs massive, in concretionary grains showing a concentric structure and in clay-like deposits. Sesquioxide of iron is usually present in considerable quantity, — sometimes to the extent of 50 per cent, — part of it replacing aluminum, and part occurring merely as an impurity. Bauxite is found in many parts of the world. One of the most interesting deposits is at Irish Hill, near Larne, county Antrim, Ireland, where it occurs in the iron measures together with lignite. At this place three layers of it are known, having an aggregate thickness of about 50 feet. The finest grade from Irish Hill is almost free from iron, containing as little of that metal as good china clay. Analyses have shown that the color of bauxite is no criterion of the freedom of the mineral from iron, since a white variety containing 3.67 per cent of Fe₂O₂ is known, while a certain strongly red variety showed, upon analysis, but 3.75 per cent, and a yellow specimen contained 14.39 per cent. In the United States bauxite occurs in considerable quantities in Saline and Pulaski counties, Ark., and in a deposit extending from Calhoun County, Ala., eastward into Georgia. Bauxite forms the principal ore of the metal aluminum. The American deposits of bauxite are well suited to the production of aluminum, as ore can be had in quantity that contains as little as 1 per cent of iron oxide, and 3 per cent of silica. Bauxite, in some localities, is undoubtedly an alteration product of basaltic rocks, while in other localities (especially in the United States) it has very likely been deposited by hot springs. The deposits of Georgia and Alabama are thought to have resulted from hot springs, the waters of which were rendered acid by passing through pyritic shales. The sulphuric acid is believed to have reacted with shale beds changing the kaolin to aluminum sulphate. As this passed on upward through limestone beds, the reaction freed Al₂O₃ as follows: Al₂(SO₄)+CaCO₃ = 3CaSO₄+Al₂O₃+3CO₂. The gelatinous Al₂O₃ was then deposited as bauxite. The Arkansas deposits are believed to be residual from the weathering of syenite. In addition to its use as an ore of aluminum, bauxite forms an important source of alum. Its clay-like form is known as wocheinite, on account of its occurrence at Wochein, in Styria. The world's product of bauxite was in 1910 about 310,000 tons; 1914 about 350,000 tons; and 1915 something over 500,000 tons; the average value in the United States being about $3 per ton. Of the 1915 production the United States is credited with 297,000 tons; France, 180,000; United Kingdom, 20,000; Italy, 10,000; Japan, 250; India, 110; all other countries, 2,600. Consult Hayes, C. Willard, ‘Bauxite’ (Sixteenth Annual Report of the United States Geological Survey, Part 3, Washington 1896); Branner, ‘The Bauxite Deposits of Arkansas’ (Journal of Geology, Vol. V, 1897, p. 263); Mead, J. W., ‘Bauxite Deposits of Arkansas’ (Econ. Geol., Vol. X, 1915, p. 28). See Aluminum; Mineral Production of the United States.