The Weathering of Rocks Under Humid Tropical Conditions.

Bauxite formation in the Pengerang Area of southeast Peninsula Malaysia is the end-product of the insitu weathering of Triassic feldspar-rich rhyolitic to andesitic lavas, tuffs and granophyre, under warm humid climatic conditions. The dominant minerals in the bauxite deposits are gibbsite, kaolinite, quartz also chalcedony, goethite, and hematite. The occurrence of bauxite is determined primarily by the parent rocks, which are typically fine-grained, rich in feldspar, and permeable to ground-water and weathering solutions. Bauxitization involves the weathering of the parent rock to a kaolinitic clay, the formation of gibbsite from the kaolinite, and the leaching of silica and iron-oxides. Modified author abstract