Abstract
AbstractOpal‐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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