herb
spending too much on rocks
Member since November 2011
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Post by herb on Mar 16, 2016 10:02:22 GMT -5
This slab has been sitting in an open box (out of sunlight) for at least 5 years. I took a look at it today and noticed that it seems to be self destructing! There is an unknown white powder on it and also a yellow powder, which I assume is sulfur. The slab was in a box with several other slabs and a sheet that has some ID's on it. From the available choices on the paper, I am guessing that this might be "Silver Lace, Barstow, CA". I haven't tried picking up the slab to see how much doesn't just turn to powder, but there are fine cracks that don't really show up in the pictures in the upper third of the slab on the right hand side, so I assume that a good chunk of the slab is toast. What I'd like to know from you experts is: Is this silver lace? Is it really silver (I'm guessing yes, by the way it is breaking down)? Can it be saved/stabilized? If not, is the powder of any value eg: can I smelt out the silver, assuming it really is silver? I know dollar wise it isn't going to be much in silver, but if it is not too hard to do, it might be cool to smelt it down and make a free form nugget type pendant out of the silver. It would give the piece an interesting story at any rate. (While typing up this post, I did a quick google search about smelting silver ore. It doesn't sound like a particularly safe thing to do!) The first picture shows the overall slab with the powder. It is about 5 or 6 inches on a side. The second picture shows the deterioration along with the white and yellow powder. The last picture shows the one corner that doesn't seem to be deteriorating yet. The grayish silver plumy areas of the slab appear to be where the white and yellow powders are forming in the rest of the slab.
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Deleted
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Post by Deleted on Mar 16, 2016 12:01:14 GMT -5
That looks like damage from an acidic environment. "Silver Lace Onyx" is not a true onyx, but a type of limey travertine. Even weak acids will start dissolving it (even if it has had a good sealer applied). The acid could be from cardboard or wood + dampness, something spilled, pvc and other plastics or even just being wet for an extended period. There may be some silver content, but it is likely not worth the cost of the energy to recover it (else it would have all dug up long ago for metal content). This material is still available, so perhaps it would be better just to get fresh stock.
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gemfeller
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Post by gemfeller on Mar 16, 2016 13:26:30 GMT -5
It's marcasite in agate from Nipomo, CA, which is known for what's called "pyrite decay" due to high humidity during storage. I've seen exactly the same kind of deterioration with my slabs from that location. Here's the Wiki explanation of the process:
"Marcasite reacts more readily than pyrite under conditions of high humidity. The product of this disintegration is iron(II) sulfate and sulfuric acid. The hydrous iron sulfate forms a white powder consisting of the mineral melanterite, FeSO4·7H2O.
"This disintegration of marcasite in mineral collections is known as "pyrite decay". When a specimen goes through pyrite decay, the marcasite reacts with moisture and oxygen in the air, the sulfur oxidizing and combining with water to produce sulfuric acid that attacks other sulfide minerals and mineral labels. Low humidity (less than 60%) storage conditions prevents or slows the reaction."
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Deleted
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Post by Deleted on Mar 16, 2016 15:40:07 GMT -5
Definitely NOT silver lace onyx.
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gemfeller
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Post by gemfeller on Mar 16, 2016 16:20:44 GMT -5
Forgot to mention that the lower right-hand portion of your last image shows unaltered material. If it's large enough it could make a nice cab with those two crystal-lined vugs. Tarnishing is normal and cabs will require cleaning/repolishing occasionally. Warning: this material is stinky (sulphur) and very messy to cut. It will leave your hands and machine black. But the results can be very worthwhile:
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Sabre52
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Me and my gal, Rosie
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Post by Sabre52 on Mar 16, 2016 18:01:31 GMT -5
Yup, I too have been visited by the marcasite gremlins. There is variation in it's resistance to moisture. The Hornitos stuff tends to be gold rich and more resistant to deterioration. Also, maybe it's just me, but it seems I experience less oxidation when the stone is polished rather than in slab form.....Mel
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gemfeller
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Post by gemfeller on Mar 16, 2016 19:12:54 GMT -5
I've noticed the same thing, Mel. But even my polished pieces seem to tarnish a litte over time and a good rub with a jewelry polishing cloth restores the original shine. I'm not familiar with the Hornitos material -- any pictures?
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Sabre52
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Me and my gal, Rosie
Member since August 2005
Posts: 20,487
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Post by Sabre52 on Mar 16, 2016 20:29:15 GMT -5
Rick, the gold bearing marcasite in the Hornitos area occurs as inclusions in the various types of jasper found up there. Don't have a lot of pics but here is one slab with an area of marcasite inclusion and in the cabs pictured, all the little specks and veins are marcasite inclusions that sparkle really nice in person....Mel
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herb
spending too much on rocks
Member since November 2011
Posts: 470
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Post by herb on Mar 17, 2016 9:56:28 GMT -5
It's marcasite in agate from Nipomo, CA, which is known for what's called "pyrite decay" due to high humidity during storage. I've seen exactly the same kind of deterioration with my slabs from that location. Here's the Wiki explanation of the process: "Marcasite reacts more readily than pyrite under conditions of high humidity. The product of this disintegration is iron(II) sulfate and sulfuric acid. The hydrous iron sulfate forms a white powder consisting of the mineral melanterite, FeSO4·7H2O. "This disintegration of marcasite in mineral collections is known as "pyrite decay". When a specimen goes through pyrite decay, the marcasite reacts with moisture and oxygen in the air, the sulfur oxidizing and combining with water to produce sulfuric acid that attacks other sulfide minerals and mineral labels. Low humidity (less than 60%) storage conditions prevents or slows the reaction." Looks like you guys nailed it! Marcasite it is! Looking at the sheet with the ID's on it, I see "NuPoma Agate California" so they just misspelled "Nipomo" I'll have to try cleaning up the slab to see how much of it is still solid. Hopefully there will be more than just that little corner left to work with. If I do cab it, I am concerned about the longevity of the cab. Is there a good way to seal or stabilize the cab so it just doesn't turn to mush in a couple more years?
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Fossilman
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Post by Fossilman on Mar 17, 2016 9:58:27 GMT -5
Hopefully you can get a piece of it for cabbing Herb!!
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Post by rockpickerforever on Mar 17, 2016 10:19:02 GMT -5
I have a few slabs of that, also a pyrite sun. Suppose I should go find them and make sure they stay in low humidity. Not so hard to do in SoCal, although it was quite humid and foggy here this morning.
Thanks for the reminder!
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