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A Kaolin-smectite interstratification sequence from a red and black complex

Published online by Cambridge University Press:  09 July 2018

C. Bühmann
Affiliation:
Soil and Irrigation Research Institute, Private Bag X 79, Pretoria 0001, Republic of South Africa
P. L. C. Grubb
Affiliation:
Soil and Irrigation Research Institute, Private Bag X 79, Pretoria 0001, Republic of South Africa

Abstract

The sequential development of kaolin by progressive alteration of smectite, involving kaolin-smectite interstratifications as a genetic link is described from a red and black complex. Mineral compositions were studied using XRD, DTA and XRF techniques. The basalt-derived soils are situated along a 600 m transect and grade in colour from dark grey (10 YR 3/1) to red (5 YR 3/3). The kaolin proportions in the interstratification increase almost linearly with increasing reddening up to ∼80%. Whole-soil chemical analyses exhibit no significant variations in the major element composition, but dithionite extractable Fe increases along the transect from 1% to 4·16%. Hematite and goethite are the only secondary iron phases. Topographic differences are slight but sub-surface bedrock contours plus appreciable variations in sand content between red and black soils could be genetically significant.

Information

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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