Bauxite Mineralogy

Abstract

Residual rocks, in which the alumina trihydrate and monohydrate minerals gibbsite, boehmite, and diaspore predominate, are classified as bauxites. Other residual minerals are developed in the unique type of rock weathering which produces bauxites, and these minerals kaolinite, halloysite, goethite, hematite, magnetite, anatase, quartz, and some phosphatic and manganiferous minerals may form the lesser constituents of bauxites. Since bauxites have formed from a variety of rock types, minor quantities of residual minerals, which occur only as traces in the original rock, may become concentrated in bauxites together with unaltered remnants of minerals resistant to weathering. Traces of the elements barium, boron, carbon, bismuth, beryllium, calcium, cesium, cerium, chromium, cobalt, copper, hafnium, gallium, gold, lanthanum, lead, nickel, columbium, magnesium, molybdenum, strontium, sulfur, tantalum, thorium, tin, uranium, vanadium, yttrium, zinc, and zirconium have been found in bauxites. Some of these elements are presumably present as secondary minerals, while others are present in unaltered mineral remnants. Quartz, ilmenite, magnetite, zircon, and rutile usually predominate as mineral remnants, and tourmaline, gahnite, xenotime, staurolite, sillimanite, andalusite, kyanite, sphene, corundum, topaz, and micas sometimes occur. In younger bauxites small amounts of alumina-siliea-hydrogels may be present, and an aluminous goethite is present in some ferruginous bauxites.