Micromorphology and composition of silica accumulations in a hardpan

The morphology and composition of silica coatings and silica impregnations in a hardpan underlying a desert loam from north-western New South Wales were examined. Optical properties and electron microprobe analyses indicate that these features were composed of opal-A. The coatings were remarkably pure, being 99.1% SiO₂. X-ray maps indicate that the silica impregnations were also calcite depletion pedofeatures. Even at high magnifications in scanning electronmicroscopy, the silica coatings had a dense, vitreous appearance with few voids. The original plant cell structure in silicified root remnants was remarkably well preserved.