Palygorskite and Sepiolite Group Minerals

The structures of both sepiolite and palygorskite contain continuous planes of tetrahedral basal oxygen atoms approximately 0.65 nm apart. The composition of palygorskite is rather variable, and comparable to that of smectite. The morphology of sepiolite is similar to that of palygorskite, and variation within the mineral species is greater than that between the species. Organo-mineral derivatives of sepiolite and palygorskite are of great interest to industry, because they have the surface and reactive properties of the grafted organic molecules but preserve the mechanical properties of the mineral framework. Indirect evidence for the pedogenic formation of palygorskite includes the compatibility of the chemical composition of water extracts from aridic soils with the stability fields of palygorskite. In calcite nodules from calcretes, palygorskite fibers may be intimately mixed with calcite crystallites, and clear identification is possible only by cautious acid etching and x-ray-diffraction analysis.