Quartz Presence in Relationship to Gibbsite Stability in Some Highly Weathered Soils of Brazil*

R. M. Weaver
Department of Agronomy, Cornell University, Ithaca, NY 14853, U.S.A.
*Agronomy Paper No. 1130. Contribution from the Department of Agronomy, New York State College of Agriculture and Life Sciences, Cornell University.

Abstract: Determination of the mineralogical composition of six highly weathered soils of the Central Plateau of Brazil showed that the sand content (predominantly quartz) was not related to the relative amounts of gibbsite and kaolinite in the clay ( < 2µm) fractions. The latter is in agreement with kinetic considerations of the involved mineral species, but in disagreement with thermodynamic considerations. However, that dissolution of quartz has been operative in these soils is indicated by an excellent relationship (r2 = 0·96) between the amount of sand-size quartz and the reactive SiO2 content of the clay fractions.

Clays and Clay Minerals; December 1975 v. 23; no. 6; p. 431-436; DOI: 10.1346/CCMN.1975.0230604
© 1975, The Clay Minerals Society
Clay Minerals Society (www.clays.org)