Log InRegister
Quick Links : The Mindat ManualThe Rock H. Currier Digital LibraryMindat Newsletter [Free Download]
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic Time
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
Keyword(s):
 
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral Quiz
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography

Techniques for CollectorsRemoving Desert Varnish

18th Mar 2007 17:25 UTCKimberly Davis

I just got back from a trip to the desert and found a lot of chalcedony, but unfortunately a lot of it is covered with desert varnish. A lot of the pieces are small and I am going to toss in my tumbler, but some of the pieces are really beautiful and have bubbles and I want to leave them in the state in which I found them. Is there any thing I can soak them in that will remove the black coating? Oxylic Acid?


Thanks for any help you can offer.


Kimberly (^o^)

18th Mar 2007 20:20 UTCAlbert Mura

If the following research is correct it might not be to easy to remove, but I guess I would try oxylic acid.


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

Thanks Albert!


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^)
 
Mineral and/or Locality  
Mindat Discussions Facebook Logo Instagram Logo Discord Logo
Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
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
Go to top of page