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Techniques for CollectorsRemoving Desert Varnish
18th Mar 2007 17:25 UTCKimberly Davis
Thanks for any help you can offer.
Kimberly (^o^)
18th Mar 2007 20:20 UTCAlbert Mura
Randall S. Perry, Imperial College, University of London, Earth Science and Engineering, South Kensington Campus, London, OX1 3 PR, UK; et al. Pages 537-541.
In many of the world's arid environments, rocks take on a shiny coating known as desert varnish. For many years early scientists, including Darwin, were intrigued by its black color and wondered at the mystery of its origin. Yet just how this lustrous veneer is created has remained a subject of controversy. A new study by Perry et al. has discovered the source of desert varnish and reveals how it can be used as a record of environmental change on Earth, and possibly on other planets such as Mars. Previously, it was thought that the activity of microbes helped to produce the rock coating. It was believed that the dark appearance is produced by the mineral manganese oxide and that bacteria exist that oxidize this manganese. This theory was strengthened when scientists discovered organic compounds and DNA fragments bound within the shiny coating. Using a battery of techniques, including high resolution electron microscopy, Perry et al. reveal that silica is the most important mineral present, indicating that biology is not important for desert varnish formation and that the source of the organic components is outside rather than within the varnish. On desert rock surfaces, silica is slowly dissolved from other minerals, then gels together to form a glaze which binds within it other substances on the rock face. Detrital grains, organic compounds, and pollutants from local environments become entombed in the coating as it forms. The desert varnish record extends through time because it occurs in fine layers that develop one over the other, over tens of thousands of years, and the deepest, oldest layers in the varnish may have formed in very different conditions than the shallowest, youngest layer. The layers represent a record of environmental change. The study also suggests that if silica exists in varnish-like coatings in deserts, caves, or hydrothermal deposits on Mars, then it may entrap ancient microbes or chemical signatures of previous life on that planet.
20th Mar 2007 01:21 UTCKimberly Davis
I tossed half of my specimens into a bucket of oxylic acid and it worked beautifully. Most of the black "crud" came off and the rest came of with a little bit of brushing with a tooth brush. I think I will toss the other half into the oxylic acid.
Thanks again!
Kimberly (^o^)
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: March 29, 2024 05:56:47