Definition of desert varnish
Desert varnish
A thin, generally dark shiny film or coating, composed of clay and admixed iron oxides and/or manganese oxides, formed on the surfaces of pebbles, boulders, and other rock fragments in desert regions after long exposure, as well as on ledges and other rock outcrops. It is believed to be caused by exudation of mineralized solutions from within and deposition by evaporation on the surface.
See also: patina
Refs.:
https://en.wikipedia.org/wiki/Desert_varnish
Potter, R.M. and Rossman, G.R. (1977): Desert varnish: the importance of clay minerals. Science 196, 1446–1448.
Dorn, R.I. and Oberlander, T.M. (1981): Microbial origin of desert varnish. Science 213, 1245-1247.
See also: patina
Refs.:
https://en.wikipedia.org/wiki/Desert_varnish
Potter, R.M. and Rossman, G.R. (1977): Desert varnish: the importance of clay minerals. Science 196, 1446–1448.
Dorn, R.I. and Oberlander, T.M. (1981): Microbial origin of desert varnish. Science 213, 1245-1247.
McInnis Canyons National Conservation Area, Mesa County, Colorado, USA