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Desert Varnish

Natural History

Desert Varnish is a dark coating found on exposed rock surfaces in arid environments. Varnish can be a prominent feature in landscapes in northern Arizona. It often coats canyon walls, particularly in the areas where water flows down the the sides of canyons.

Native Americans created petroglyphs by scraping or chipping away the dark varnish to expose the lighter rock beneath. 

The coating is composed dominantly of fine-grained clay minerals that attach to the wall via airborne dust. In the clay layer, black manganese oxide (the mineral birnesite) and red iron oxide (the mineral hematite) add color.  

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