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Removing Lichens

Posted by John Collins  
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John Collins January 22, 2012 03:39PM
Hi,
I got this (what could be nice) sample of quartz crystals imbedded with realgar (Peru) the other day and was dismayed to find to see these deposits on parts of it. I'd like to clean them off..
Has anyone had experience cleaning lichens off minerals. Would bleach do it? Ultrasound?
open | download - P1030248web.jpg (117.7 KB)
open | download - P1030249web.jpg (81.7 KB)
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Woody Thompson January 22, 2012 03:57PM
Hi John,

Bleach usually works good for removing organics such as lichens, moss, etc. I don't know whether it would have any effect on realgar, so maybe you could try it on a small part of the specimen first.
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Alfredo Petrov January 22, 2012 04:10PM
If the organic stuff is too tough for bleach, you can remove it with NaOH solution (caustic soda; "Drano"), but that will definitely destroy the realgar too (unless the realgar is included in the quartz).
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George Eric Stanley Curtis January 22, 2012 04:49PM
I once lost a good sample of Torbernite because I tried to clean it with bleach. The Torbernite dissolved.

Whatever you use it on, it is wise to try a small section first.

Eric

United Kingdom, Cornwall
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John Collins January 22, 2012 04:55PM
I certainly worry about the chemical effects of bleach on realgar and orpiment. Ultrasonic cleaners seem cheap ($34.95) for my purposes so if I don't learn of any concerns, I'll go that route.

John
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David Von Bargen January 22, 2012 05:02PM
Are you sure that these are lichens and/or realgar? Growth to any size would take a fair amount of time in sunlight and the realgar should have been altered/destroyed.
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John Collins January 22, 2012 05:52PM
Any realgar (if it is there) is represented by yellow stains on what must have been the underside and small deposits on the sides of the specimen
My rock would look like:
http://www.mindat.org/photo-319192.html

if it were clean of surface stuff.

John
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Steve Hardinger January 22, 2012 06:12PM
I am dubious that a living organism (lichen) could have grown in such as toxic arsenic-rich environment (i.e., around all that realgar). Then again, nature does some interesting things.

In my experience yellow-green, amorphous material associated with realgar, especially on Palermo Mine material, is in fact, orpiment.
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John Collins January 22, 2012 07:45PM
Steve,
I just looked at the surface deposit on the small crystals with my microscope and it appears to be a secondary growth of clear microcrystals (probably quartz). Imbedded in this are black crystal clusters of a semimetallic appearance. All very interesting!
The yellow deposits are also certainly crystalline and so are most likely orpiment.

I had wondered whether my specimen had been sitting out on the exposed ground for some time before being collected.

I'm starting to like the idea of secondary growth more and more. But the appearance is different in this regard from the mindat photo of much the same mineral deposition.

John
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