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rock varnish |
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rock varnish [′räk ‚vär·nəsh] (geology) A dark coating on rock surfaces exposed to the atmosphere. It is composed of about 30% manganese and iron oxides, up to 70% clay minerals, and over a dozen trace and rare-earth minerals. Although found in all terrestrial environments, it is mostly developed and best preserved in arid regions. Also know as desert varnish. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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] National Laboratory, one of the researchers performing rock varnish work for the Energy Department studies, acknowledges that "calibration techniques are a problem. Rock varnish is a black, paper-thin coating that forms slowly over tens of thousands of years as clays, trace elements, organic matter and whatever other particulates happen to fall out of the air are cemented to rock surfaces by iron and managanese oxides. |
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