Rock varnish microlamination dating
It is made up of clays and iron and manganese oxides.
As such the chemical composition of the varnish is different from that of the rocks on which they form and thus the components, especially manganese, of the varnish must be derived from air-borne dust and rainwater.
Dark layers in varnish are rich in Mn and Ba, but poor in Si and Al.
Orange and yellow layers are poor in Mn and Ba, rich in Si and Al.
the white crystals at the bottom is the original rock surface.
The layering pattern indicates different chemical compositions (see below for more examples) It may be hard to believe but bacteria are able to live on the surface or at least the upper few millimeters of the rock matrix under extreme temperatures and desiccation.
Rock varnish is much more than just chemicals that leached out of material above and ran down than surface of a rock leaving a stain.
Rock varnish is a layer (sometimes hundreds of layers ) of mostly inorganic material that builds up on the surfaces of rocks that are found in environments where very little erosion occurs.
Rocks on the surface of the ground sometimes can form something called desert pavement and the surfaces of those rocks may also become covered with desert varnish.
The origins of desert varnish have long defied full explanation.
Rock varnish “grows” on rock surfaces rather than simply staining the rock surface. There is still much to learn about rock varnish but it is clear that rock vanish comes in many different forms differentiated usually by their chemical makeup.