The manganese and iron
oxide
mineralogy of desert varnish
Russel M. Potter and
George R. Rossman
Division of Geological and Planetary
Sciences
California Institute of Technoogy
Pasadena, CA 91125
Abstract
Bimessite and hematite have been identified as the Mn- and Fe-oxide
phases in desert varnish by IR spectroscopic and chemical techniques.
These oxides are in intimate physical association with the mixed-layer
illite-montmorillonite clay minerals of varnish. An abrupt change in
chemistry, mineralogy and morphology exists at the varnish-Tock
interface. The origin of the
material appears to be external to the rock which it coats. The oxides
appear to be transported by water, and it is most likely that the clays
are trans ported by wind or water. Clay minerals are necessary for
varnish formation, probably through their influence on oxide
concentration or deposition.
last updated: 5-Oct-2020