Home Desert Varnish Desert varnish is the thin red to black coating found on exposed rock surfaces in arid regions.
Varnish surfaces tend to be shiny when the varnish is smooth and rich in manganese.
Desert varnish consists of clays and other particles cemented to rock surfaces by manganese emplaced and oxidized by bacteria living there. It is produced by the physiological activities of microorganisms which are able to take manganese out of the environment, then oxidize and emplace it onto rock surfaces. These microorganisms live on most rock surfaces and may be able to use both organic and inorganic nutrition sources. These manganese-oxidizing microorganisms thrive in deserts and appear to fill an environmental niche unfit for faster growing organisms which feed only on organic materials. The sources for desert varnish components come from outside the rock, most likely from atmospheric dust and surface runoff.