What is desert varnish Desert varnish is a dark coating on rocks found in arid regions. The coating is composed dominantly of fine-grained clay minerals. Within the clays are black manganese oxide and red iron oxide. A more general term is rock varnish which applies to dark coatings on rocks in general.
Varnish can be a prominent feature in many landscapes.
Desert varnish plays an important role in archeology. Desert varnish is commonly seen coating rocks in deserts. The older slides have a more mature coating of varnish. Well-developed coatings can form in the splash zone of rivers in arid regions. The portion of the rock above the line sits above the level of the desert pavement.