How long does an application of nail polish last? Regular nail polish begins to chip after few days. Gel polish supposedly can last up two to three weeks. But imagine a polish that can last for hundreds or even thousands of years? There is such a polish and it is found on rocks in deserts throughout the world, including the deserts of the southwestern US. It’s called “Desert Varnish”.
Last week, my husband and I visited White Tank Mountain Regional Park near Phoenix, AZ. There we came across several examples of petroglyphs, rock etchings made by Hohokam Indians, who lived there until around 1100 A.D. Some ancient petroglyphs found there may be up to 10,000 years old.
According to Dr. Jeff Mitton at the University of Colorado, desert varnish “is a thin veneer of clay, minerals and microbes that forms on the surface of rock. It accumulates slowly, at a rate of 1 to 40 micrometers or less than the width of a human hair in 1,000 years.”
The colors of desert varnish range from black to red, depending on the relative proportions of iron (red) and manganese (black). Given the colors we saw at White Tank Mountain, I suspect both minerals were present.
How desert varnish forms is still open to debate. One group of hypotheses involve biological organisms, such as microbes and fungi. The other group of hypotheses are abiotic, in that living organisims are not required. Perhaps the mechanism depends on environmental conditions; perhaps there is more than “one way to skin this cat”.
But one common factor is the presence of manganese. According to this Dr. Ronald Dorn in his book, “Geochemical Sediments and Landscapes”, “Desert varnish accumulates only when and where nanometre-scale fragments of manganese,… cements broken and decayed fragments of clay minerals to rock surfaces.”
Now if there were only a way to produce desert varnish in a variety of colors. I like the idea of long lasting nail polish, but given a choice, I’d prefer a darker shade of pink.
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Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at email@example.com for time and place.
Wednesday mornings, January 30; February 6, 13, 20, & 27.
Saturday mornings, February 2 & 16.
Saturday, February 16, 8:00 – 10:00 AM. “Wild Birds of February” at Towsley Canyon. Meet in the front parking lot at the gate. Click here for a map and directions.
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