John L. Arola

Publication Date


Document Type


First Advisor

Goldich, Samuel S., 1909-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology


Bauxite; Laterite


Laterite and bauxite, the commercial aluminous variety, are formed under a tropical to subtropical climate. The most favorable and common parent rocks are of basaltic and phonolitic composition. Laterites form under conditions of good drainage, hence, moderate relief is essential. The primary lateritic profile is characterized by oxides and hydrous oxides of iron and by the bauxite minerals, gibbsite and boehmite, above the water table and clay minerals below where conditions are less favorable for the removal of silica. Once the primary lateritic profile has been formed, it is subject to profound changes that involve concretionary action and the separation of iron and alumina. Gibbsite concretions in clay are of various size and shape. They include nodules, branching or bulbous rod-like concretions, and sheets or veins of considerable extent and variable thickness. The complex chemistry of weathering and lateritization involves the reactions that take place at the mineral-groundwater interface and in the larger rock-groundwater system. The transition from bauxite at the surface to clay and parent rock at depth is a natural consequence of the development of a water table. Rapid groundwater movement above the water table removes soluble weathering products and small clay particles, whereas, the more sluggish groundwater movement below the water table flavors clay minerals. Mixtures of clay and gibbsite are developed particularly in the zone of the fluctuating water table.


Includes bibliographical references.||Includes illustrations and maps.


iv, 69 pages




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