Lapidaryforum.net
Let's Rock => Mineral Specimens => Topic started by: jerrysg on October 02, 2016, 03:03:00 PM
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We collected quartz at the Fat Jack mine in Arizona a couple of weeks ago. This is a photo of our best one (long dimension of plastic base is 1.5") after about 5 days in oxalic acid to remove the iron stains.
But a problem developed after about a week in the oxalic acid solution. The specimens in both of the containers developed a bright yellow coating. Almost the color of sulfur. The coating resists coming off with a toothbrush or a stiff nylon brush although a fingernail will remove some. Works on the single crystals but obviously not on the clusters. Changing the oxalic acid for fresh using distilled water did nothing.
Anyone know what the precipitate is and how to remove it? Would using an ultrasonic bath help?
Jerry
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That's iron oxide being redeposited on your crystals. Watch the color of your acid. When it starts to turn yellow, take your stones out & put them in clean water. Neutralize your acid with baking soda & dump it. Make a fresh batch of acid & put your stones back in to finish cleaning them.
Use only a plastic or ceramic container for your acid soak. If you use a metal bucket the acid will attack the metal. The resulting deposits on your crystals will be even worse than what you have now.
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Thanks Jake,
Always in plastic containers! I went with fresh acid made up with distilled water and there has been no change with the yellow ppt.
Heat or ultrasound make any difference?
Jerry
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Found out that the precipitate is calcium oxylate and I caused it because I made up the oxalic acid solution with tap water instead of distilled water. Our water here in AZ is very high in calcium. Fortunately the precipitate is very soluble in muriatic acid (HCl). Cleaned all the samples overnight in the HCl and then back in the oxalic acid solution made up with distilled water this time. Here's the double scepter after the dual acid treatment.
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Good to know and glad they came out okay! I had the same thing happen using well water with a high mineral content a couple of years ago. Thanks for posting the cause and what to do about it.
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Very nice and will keep that in mind! Ridiculous calcium content here too.
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AZ is known for ridiculous amounts of dissolved minerals in the water. I have a reverse osmosis system going just to be able to drink the darn stuff. If I have to add water to anything around here in a recipe or for something I'm creating, I use the water from the reverse osmosis - it saves me a lot of headache. Last year I made two batches of homemade laundry detergent. One was with RO water, the other with ordinary tap water. You wouldn't think it would make that much difference. The soap made with tap water clouded up faster as it cooled and gelled up faster as well and turned into a paste, whereas the stuff made with the RO gelled up but didn't get paste-like.
I'm glad you were able to solve the problem. :icon_sunny:
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I use to live in the Northwest corner of Louisiana and the only digging I got to do the whole time I lived there was crystal digs up in Arkansas. We used Iron Out to clean all of our crystals and it worked great. You can get that at any Home Depot or Lowe's and you don't have to worry about neutralizing it. Even with the Iron Out though, you want to gage how long you leave the crystals in the solution because it will create a film on the surface if left too long. We usually let them stay in the solution for about 3 or 4 days, then check. A plastic tub for the Iron Out is also best I think. When we were done, we put a hose in the tub and let it run over until it was diluted good then dumped the rest down the bathtub, kill two birds with one stone and clean the pipes while we were at it! I learned this trick from an Uncle up in Idaho that said that is how all the old timers up there do it! They don't use that industrial acid. Plus it is less expensive which is always good!
GatorGal