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Identity HelpID coating on crystals

10th Jun 2015 07:27 UTClyn de

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Can you help ID the coating that is on these crystals? They were found in a pocket in an old silver or maybe galena mine in the Comstock Lode area in Storey County , NV. We were wondering if the black coating could be silver sulfide? Thank you.


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10th Jun 2015 12:41 UTCPaul Brandes 🌟 Manager

Welcome to Mindat, lyn de!

Possibly.... but could also just be a coating of manganese oxides as well; hard to say from just a photo. :-S

10th Jun 2015 14:53 UTCKyle Beucke 🌟

Hello. I would say it is very unlikely to be a silver mineral. This is not a habit I am aware of for acanthite (heck, never heard of ANY silver mineral forming an even coating on quartz crystals, maybe as a supergene coating on pyrite), and it doesn't look like the typical occurrence of that mineral there (in quartz vein material with base metal sulfides and pyrite).


Manganese sounds like a good bet.


Kyle

10th Jun 2015 19:10 UTCMark Heintzelman 🌟 Expert

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Ii would tend to agree with Manganese Oxides (black), with Iron oxides (orange) as well. For some good examples of these kind of coating, some examples quite similar to yours as well, you might want to look through the image gallery for the Diamond Hill Quartz mine in South Carolina, which is well known for these Manganese Oxide coatings and has produced quite a lot of decent examples more recently.


These coatings can actually give ordinary quartz a rather interesting visual appeal. This example, which I acquired from Matt Price just last year, has an interesting, sharply restricted zone of Manganese Oxide deposition running through the center of the piece, which I personally found rather appealing. :D


MRH


11th Jun 2015 06:42 UTClyn de

Thank you for your ideas! I will take the pieces to a local college and tell them what you suggested. It appears the crystals formed and this stuff dripped down on them...and since it was a silver mine, ...well, easy thought to put together. Darn.

Nice piece from Diamond Hills!!
 
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