[Rockhounds] Cleaning quartz and geodes

[Erich Kern]

I've found by experience it's all about how well you rinse the piece. By "rinse" I mean a long soak. There are tiny cracks and crevasses where the acid is trapped. As the piece dries, the acid creeps out. This is true whether I've used acid or Iron Out which is vastly superior to HCL or oxalic acid for removing rust stains.

Large specimens I've soaked for 2 days in a bucket, changing the water at least every 12 hours; more often if you can. Recently I was surprised that a large piece of native copper I cleaned needed an overnight soak in fresh water to prevent a color change after it dried. I wouldn't think native copper could retain some chemical residue even after distilled water cleaning in an ultrasound tank, but the overninght soak cured the problem. Add a few drops of 'Joy' liquid detergent to the rinse water. It lowers surface tension and allows the rinse water to penetrate tiny cracks. 

Cheers,
Erich Kern
Murrieta, CA

----- Original Message ----- 
From: Joshua Stiff 
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors 
Sent: Tuesday, September 16, 2008 12:48 AM
Subject: [Rockhounds] Cleaning quartz and geodes


I have been cleaning Lolo smoky quartz specimens and Challis volcanic
agates/geodes using muriatic acid.  The results have been mixed.
Sometimes the specimens come out beautifully, while other times I end
up with a yellow staining.  I've tried re-bathing the specimens in
muriatic, and again, sometimes this helps, sometimes it doesn't.  Its
really bizarre to me as I can't pin-point any concrete similarities as
to why the staining occurs.  My best guess is that depending on what's
reacting in the load I am washing, perhaps the temperature in the
specimen's matrix increases enough with the reaction to allow acid to
permeate the specimen?  I would assume then, when the acidic reaction
stops, HCl is trapped inside the specimen causing yellow staining?  I
am no chemist so its a guess :)

Anyways, advice would be helpful.  I've googled the topic multiple
times and have found many "becareful when working with acid topics".
I understand that this probably means I should be a chemist before
playing with acid :)  However, considering that I am using the HCl
with the proper safety equipment (as directed from many different
sources), it would be nice to find more advice on how to properly
clean quartz minerals with HCl.  I've tried 27% HCl at 100%, and a
50:50 mix with distilled water.  I also have my baking-soda/distilled
water rinse mix ready.  Still, the yellow staining has occurred at
least once in every batch I've tried.

Sincerely,
slightly frustrated
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