About Us | Help Videos | Contact Us | Subscriptions
 

Abstract

 

This article in SSSAJ

  1. Vol. 49 No. 5, p. 1297-1302
     
    Received: July 9, 1984
    Accepted: Mar 27, 1985


 View
 Download
 Alerts
 Permissions
Request Permissions
 Share

doi:10.2136/sssaj1985.03615995004900050045x

Biotite Kaolinization in Virginia Piedmont Soils: II. Zonation in Single Grains1

  1. W. G. Harris,
  2. L. W. Zelazny and
  3. F. D. Bloss2

Abstract

Abstract

Kaolinized zones in soil biotite grains were investigated by x-ray diffraction (XRD), microprobe, and optical methods. These zones displayed microcrenulations and thus a dulled luster on (001) cleavage surfaces. Compared to unaltered biotite, kaolinized zones were lighter in reflected light but darker in transmitted light, probably because the crenulated (001) surfaces diffuse light. Kaolinized/unkaolinized interfaces in some grains were roughly perpendicular to (001) cleavage. This suggests that kaolinization proceeds inward from the grain edge along a multilayered front by a topotaxial rather than epitaxial reaction. Kaolinized zones contained islands of residual biotite and had an optic axial angle (2V) and dispersion more consistent with biotite than kaolinite. Biotite-derived kaolinite grains contained Fe, which was either structural or occluded, and had Si/(Al + Fe + Mg + Ti) ratios >1.0. A significant vermiculite intermediate phase is not essential for kaolinization, as indicated by the lack of XRD evidence of vermiculite as well as by the simultaneous loss of K and divalent octahedral cations in examined biotite/kaolinite grains.

  Please view the pdf by using the Full Text (PDF) link under 'View' to the left.

Copyright © . Soil Science Society of America