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