Rock varnish microlamination dating
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.
I expect that most people simply look at these dark streaks and think they are simply stains like a stain on a cement driveway or that line of rust color running down a wall from a rusty nail above. But what if you were shown a picture of the same rock taken 50 years earlier and the stains looked identical to you?
The microlaminations can be observed when varnish is shaved thin enough (5-10 µm) to see through with a light microscope.
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.