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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

Leoncio A. Garza-Valdes
Affiliation:
Rosa Verde Tower, 343 W. Houston St., Suite 612, San Antonio, TX 78205
Brian Stross
Affiliation:
Anthropology Department, University of Texas at Austin, Austin, TX 78712
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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].

Type
Research Article
Copyright
Copyright © Materials Research Society 1992

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