Below the ground line band in the region where the rock is buried below the surface, an orange coating develops. Here you can see how the entire underside of the rock is coated with the red coating The composition of desert varnish Desert varnish is dominantly clay. The clay minerals represent the clays found locally in the region where the varnish develops. Layering in the clays can be seen to follow the contour of the underlying rock. The clays appear to be derived from airborne dust.
Varnish has a sharp contact with the underlying rock.
The sample was prepared by fracturing a thin slab of a varnish-coated rock. The exposed surface filling most of the frame is a fracture through the varnish layer. A portion of the underlying rock surface can be seen in the lower left portion of the image. Note how the varnish smoothly goes around the rounded mineral grain in the bottom center-right side of the image. Things which look like varnish but which are not Counterfeit manganese deposits can take various forms.