rock varnish

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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
Mentioned in ?
References in periodicals archive ?
The rock varnish revolution: New insights from microlaminations and the contributions of Tanzhuo Liu.
Rock Varnish. En Geochemical Sediments and Landscapes, editado por D.J.
Experimental approaches to dating petroglyphs and geoglyphs with rock varnish in the California deserts: current status and future directions.
Los Alamos post-doctoral researcher Nina Lanza has previously studied rock varnish on Earth rocks.
"Rock varnish on Earth is not clearly understood," Lanza said.
An investigation of the rock varnish showed varying levels of thickness and lead contamination.
In the Lower Pecos, two distinct forms of rock accretions cover the limestone rock surfaces: a dark gray to black rock varnish coats areas that are directly exposed to rain and rain run-off while a light brown crust forms in more sheltered areas.
Harrington from the Los Alamos [N.M.] National Laboratory, one of the researchers performing rock varnish work for the Energy Department studies, acknowledges that "calibration techniques are a problem." Yet, he says, it will take much more research to tell whether either of the controversial calibration methods yields inaccurate results.
The team found bacteria associated with rock varnish in an area where the surrounding soils were essentially devoid of life.
Rock varnish is an extremely slow-growing coating that forms on the surfaces of rocks in arid and semiarid climates.
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.
Dorn has published a few papers showing how rock varnishes record the alkalinity of past environments, as well as how varnishes can be used to date geologic and archaeological objects.