ABSTRACT
This chapter discussES the evidence for a biological origin for desert varnish. Evidence indicates that desert varnish is formed by an accretional process in which airborne dust serves as the principal source of the elements in the coating. These deposits are superficially similar to desert varnish, but typically are different in mineralogy. There is now abundant evidence that a variety of microorganisms inhabit desert varnish and desert rocks and soils. The desert varnish in the Mojave Desert near Stoddard's Well in California was described in detail by Laudermilk. Consequently, particular attention has focused on determining the presence and concentrations of manganese-oxidizing bacteria in desert varnish. Evidence for the involvement of micro–colonial fungi in desert varnish formation is observational. To realize the full potential of desert varnish as a paleoenviron-mental indicator, it is necessary to understand more fully the mechanisms of formation and alteration of varnish and the responses of the mechanisms to environmental conditions.
