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This article in SSSAJ

  1. Vol. 51 No. 4, p. 982-985
     
    Received: Apr 21, 1986
    Published: July, 1987


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doi:10.2136/sssaj1987.03615995005100040029x

Silica in Duric Soils: II. Mineralogy1

  1. O. A. Chadwick,
  2. D. M. Hendricks and
  3. W. D. Nettleton2

Abstract

Abstract

Opal-A and opal-CT were identified by x-ray diffraction as the primary pedogenic silica minerals in two central Nevada duric soils. Opal-A was also present in the form of allogenic volcanic glass. Pedogenic microcrystalline quartz was not identified. Saturated paste extracts contained > 60 mg L−1 Si(OH)4 and opal-A precipitation is likely during soil dehydration. Opal-CT precipitates from soil solution once silica concentrations have been reduced through adsorption, precipitation, and/or increased solution ionic strength, or it may be produced by transformation from opal-A by mineral aging processes. High concentrations of silica in soil solution favor opal formation in preference to deposition of microcrystalline quartz.

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