THE MICROMORPHOLOGY OF GIBBSITE FORMS IN SOILS

Summary Using optical and scanning electron microscopy various forms of gibbsite are described in some tropical soils. In a lateritic soil from Zaire gibbsite occurs on argillans, in randomly oriented crystal sheets, as nodular aggregates infilling vughs and on ped faces. The mineral also surrounds quartz grains and kaolinite pseudomorphs after biotite. In other soils gibbsite occurs as silt-size particles disseminated through the matrix, as large nodular aggregates, and as anatomizing sheets associated with crystal chambers. It is clear from these observations that alumina must be a mobile constituent and was probably translocated through the soil in solution.