Desert varnish
Esquema
Jerarquía
<materiales por función> > revestimiento (material) > <recubrimientos por composición u origen>
Descripción
Thin mineral coating composed of iron and manganese oxides deposited on rock surfaces in desert areas. The reddish brown or black desert varnish layers form as moisture evaporates leaving behind dissolved mineral residue which wind abrasion polishes over the course of centuries. Some petroglyphs are images incised in desert varnish, a technique which exposes the lighter stone beneath.