Desert Varnish

Desert varnish is the thin red to black coating found on exposed rock surfaces in arid regions. Varnish is composed of clay minerals, oxides and hydroxides of manganese and/or iron, as well as other particles such as sand grains and trace elements. The distinctive elements are Manganese and Iron. The color of rock varnish depends on the relative amounts of manganese and iron in it: manganese-rich varnishes are black; manganese-poor, iron-rich varnishes are red to orange; those intermediate in composition are usually a shade of brown. Varnish surfaces tend to be shiny when the varnish is smooth and rich in manganese. Thousands of years are required to form a complete coat of manganese-rich desert varnish so it is rarely found on easily eroded surfaces. Also known as Patina. (NPS - SAGUARO)

Desert varnish streaks on the entrance to Fay Canyon, Sedona