Answer:
desert varnish
Explanation:
Desert varnish
Also called the rock varnish ,
It is the orange -yellowish to blackish coating which is found on the surface of rocks in the arid environments .
It is about a micrometer thick and have a nanometer - scale layering on the surface .
desert varnish is formed only over the surface of the physically stable rocks.
The composition of the varnish is from iron , and manganese oxides .
