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Desert Varnish of the Sonoran Desert: Optical and Electron Probe Microanalysis

1978; University of Chicago Press; Volume: 86; Issue: 6 Linguagem: Inglês

10.1086/649741

1537-5269

Carlton C. Allen,

Geochemistry and Geologic Mapping

Optical and electron probe microanalysis of the dark patination coating rocks from the Sonoran Desert reveal a distinct, though sometimes discontinuous layer approximately 20 microns thick. This layer is characterized by concentrations of iron, manganese and magnesium considerably higher than their concentrations within the host rocks. The metal-rich layer is contained within a clay-like matrix and is, in some samples, separated from the host rock by a weathering cortex up to 1 mm thick. A large fraction of the metal in the outer layer appears to have been derived from sources external to the varnished rocks, probably wind-transported dust and clay.