concentrations of iron and manganese, there are no significant modern uses of desert varnish. However, some Native American peoples created petroglyphs by scraping or chipping away the dark varnish to expose the lighter rock beneath. Desert varnish often obscures the identity of the underlying rock, and different rocks have varying abilities to accept and retain varnish. Limestones, for example, typically do not have varnish because they are too water-soluble and therefore do not provide a stable surface for varnish to form. Shiny, dense and black varnishes form on basalt, fine quartzites and metamorphosed shales due to these rocks' relatively high resistance to weathering. Its presence has been cited as a key factor in the preservation of a large number of petroglyphs dating back to the Iron Age and earlier in areas such as the Wadi Saham in the United Arab Emirates. See also References External links Desert Varnish Rock Varnish (desert varnish): An Internet Primer for Rock Art Research by Ronald I. Dorn, Professor of Geography Arizona State University DESERT VARNISH (rock varnish) New Way Suggested to Search for Life on Mars — Space.com Researcher: Mars rock varnish hints of life July 2, 2001 By Richard Stenger CNN Rock Varnish As A Habitat For Extant Life On Mars Deposition (geology) Sedimentology Deserts Rocks Hypothetical life forms