The relationship between ventral rubification, rock size, and age shown in this study suggest that stable land surface environments (i.e., stable landforms and large surface rocks) create conditions needed for strongly expressed varnish.In the absence of traditional dating techniques, these relationships could be used to estimate the ages of Mojave Desert landforms.One of the most common places to find rock varnish is in deserts were this varnish is called desert varnish.Desert varnish appears on the vertical surface of rocks but it may also appear on very stable horizontal surfaces.Desert varnish is a commonly occurring feature on surface rocks of stable landforms in arid regions.The objectives of this study were to investigate how desert varnish is related to the properties of the rocks on which it forms and how varnish is related to landform surface age and stability.Varnish can be a prominent feature in many landscapes.
You might start to wonder just how old those stains are on those rocks.
When V horizons were present, the varnish tended to be strongest near the lower boundary of these horizons.
This interaction between the V horizons and location of maximum varnish expression on the rock may be due to the effect of V horizons on infiltration and the retention of water at those depths.
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.