The Nature of Anauxite*

Robert B. Langston and Joseph A. Pask
Department of Mineral Technology University of California, Berkeley, California
* Part of a dissertation presented in partial fulfillment of the requirements for the degree Doctor of Philosophy, September 1967. The work was partially supported by the State of California Division of Mines and Geology and by the National Science Foundation, Grant G-9435.

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 Ione 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: 2⋅01±0⋅04 Si O 2 :A l 2 O 3 :2⋅09±0⋅09  H    O 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.

Clays and Clay Minerals; January 1969 v. 16; no. 6; p. 425-436; DOI: 10.1346/CCMN.1969.0160604
© 1969, The Clay Minerals Society
Clay Minerals Society (www.clays.org)