The Nature of Anauxite

Abstract

Anauxite crystals are reported to contain a higher SiO₂:Al₂O₃ ratio than the 2:1 ratio found in kaolinite. A structure proposed for anauxite places the excess silica in double silica sheets, but an exact structure for anauxite has never specifically been determined. Many workers believe that anauxite is kaolinite associated with some extremely fine-grained excess silica which is not a part of the structure. Eight specimens studied in this work included portions of type materials from Bilin, Czechoslovakia, and the lone formation in California.Amorphous silica and alumina are readily soluble in boiling (N/2)NaOH. Kaolinite is only slowly soluble in this reagent, but becomes readily soluble after dehydroxylation. Weight loss, differential solution rate, kinetic and X-ray diffraction studies were used to establish that the kaolinite clay fraction in the anauxite specimens had the composition of: \$ Some of the anauxite grains are single crystals, while others are aggregates. The latter appear to be bound together by an amorphous silica phase. Hot caustic leaching extracts the amorphous silica and breaks up the aggregates producing “fines.” Improved characterizations of minor impurities were obtained when the residues from hot caustic treatments were studied with X-ray diffraction techniques.