Desert varnish
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Description
A thin, shiny, reddish-brown or black coating that forms on the surface of exposed rock surfaces in arid regions throughout the world (Elvidge and Moore, 1980). Desert varnish layers are the result of several thousand years of physical, chemical, and biological weathering. Their thicknesses typically range from 10-200 micrometers. The coating is primarily composed of clay minerals with small amounts of iron and manganese oxides. Petroglyphs were created by carving images and patterns in the desert varnish layers to exposed the lighter color stone beneath.
Resources and Citations
- C.D.Elvidge, C.B.Moore, "Restoration of Petroglyphs with Artificial Desert Varnish" Studies in Conservation, 25:108-117, 1980.
- Rock Varnish at http://www.annettelamb.com/nature/rocvarnsh/index1.htm
- Wayne's world: Desert Varnish and Lichen at http://waynesword.palomar.edu/pljan98.htm#Desert