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Rock Varnish on a Pre-Columbian Green Jasper From the Tropical Rain Forest (The Ahaw Pectoral)
Published online by Cambridge University Press: 28 February 2011
Abstract
With aging, many rocks surfaces not in direct contact with the soil, develop a black coating. This deposit has been given different names: desert varnish [1,2], rock varnish [3], and biogenic rock varnish [4]. The rock varnish is a dark coating, usually 10 to 30 micrometers thick, with a variation from a few micrometers to over 500 micrometers [5]. It is composed of manganese and iron oxides, silica, and clay minerals. A similar type of coating is accreted in pottery found in ancient tombs [6].
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