Abstract: High-alumina minerals refer, in this paper, to Al-rich, normal sedimentary phases, including gibbsite, boehmite, diaspore, possibly “proto-diaspore” and “proto-alunite”, “Al-chlorite”, and corundum, in association with kaolin minerals. They may be derived from any common Al-containing rock. Processes of origin include direct bauxitization of non-clay silicate minerals and rocks, and the desilication of any of the common clay minerals, particularly of the kaolin group. Apparently aluminous gels were formed within certain marshy basins, and/or were transported into basins, giving rise to concretionary masses of high-alumina minerals. Concretionary deposits were formed by dissolution of Al and reprecipitation.
Alumina is probably more soluble, inherently, than is interpreted from geologic occurrences. Even after Al is dissolved under appropriate pH, or complexing reactions, its solubility is obscured by Al-immobilization through fixation within 3-layer clay minerals, or absorbed by other phases. A 14Å phase, probably aluminous, is not uncommon in certain soils, and in flint and boehmite-diaspore-containing clays. Subtraction of silica by plants, is accompanied by concentration of alumina.