ampeg
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Post by ampeg on Oct 18, 2018 2:10:05 GMT -5
I don't have a clue what these stones really are. I was told they are Alexandrite-----they are extremely hard, Silicon Carbide wouldn't even scratch them, so I had to buy flat lap equipment (Ameritool 8"), and the diamond discs did work on these stones. There are black areas that did take a shine, and there are dark grey areas that would not take a shine. The biggest one is 37.461 grams; the others are 29.869, 21.569, and 20.748 grams. They don't appear to change color at all. Is there an "industrial" grade of Alexandrite? I would be thrilled to find out what these stones actually are. Thanks in advance for any help you might be able to render.
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Deleted
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Post by Deleted on Oct 18, 2018 11:36:49 GMT -5
There is opaque alexandrite/chrysoberyl, but silicon carbide should scratch it. Alexandrite is just chrysoberyl that has the color change (warm incandescent light vs. cool fluorescent light). If silicon carbide isn't scratching it, I'd suggest corundum/sapphire as a possibility, or even carbonado diamond.
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ampeg
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Post by ampeg on Oct 18, 2018 14:50:31 GMT -5
thanks, rocks2dust!
I've never heard of corundum sapphire or carbonado diamond, so I'll do some research on those.
I ran these all the way through 80 grit diamond, up to 14,000 grit diamond paste. Many, many micro-pits, creases and cracks, but ended up with only 36% grinding loss.
I was sweating every minute of it, too, because I was told they could be valuable, and this was the first time I had processed stones of any kind.
It was like learning to play with firecrackers by handling dynamite.
They're not my stones, but I need to help the owner figure out who/where/how to sell them.
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Post by MsAli on Oct 18, 2018 14:59:17 GMT -5
I think it is really important in identifying something to state location of where they were found
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Post by MsAli on Oct 18, 2018 14:59:35 GMT -5
also it might help to show these wet
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Post by pauls on Oct 18, 2018 15:43:30 GMT -5
Here's the Wiki for Chrysoberyl including Alexandrite. en.wikipedia.org/wiki/ChrysoberylThe main thing with Alexandrite is its strong pleochroism (colour change) It turns red in incandescant light, so if your stones are colour change they are Alexandrite. Specific Gravity 3.5-3.84 It has a hardness of 8.5, just softer than Silicon Carbide at 9 - 9.5 so it should be possible to cut Alexandrite with SiC. My thought would also be Corundum, eg Green Sapphires, at hardness 9 can't be cut with SiC. Specific Gravity 3.95-4.10 So probably your best bet would be to do a Specific Gravity test. You need a set of accurate down to .001 gram scales to get a reasonable chance of getting an accurate result though. Get along to your nearest gem club there's usually knowledgable keen people there that would be able to help you.
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ampeg
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Post by ampeg on Oct 18, 2018 16:43:23 GMT -5
alikat218,
Thanks for your reply!
These are from Brazil.
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ampeg
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Post by ampeg on Oct 18, 2018 16:44:48 GMT -5
alikat218,
Unfortunately, I have already shipped these back to the owner, so I won't be able to supply a picture of them wet.
I'll inquire about having him wet them and shoot a picture on his end.
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ampeg
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Post by ampeg on Oct 18, 2018 16:54:05 GMT -5
pauls,
Thanks for your reply,
I tumbled these for a week in 60/90 Silicon Carbide----it was if nothing had happened.
So, I ordered in 43/70, and tumbled them for a couple of days in that-----same non-result.
Then, I bought the flat-lap equipment, and also an 80 grit diamond disc (in addition to the standard colored diamond discs that came with the Ameritool machines), and finally started getting results.
I don't have a specific gravity rig, but I will begin researching those tonight.
I would have to have the stones shipped back to me to be able to test their specific gravity.
There is no gem club in my town that I have been able to find----there used to be one that was sponsered by a rockhound shop back in the 1980's, but the owner passed away and the club seems to have disappeared.
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ampeg
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Post by ampeg on Oct 19, 2018 14:14:49 GMT -5
I forgot that I had some of the same stones here, that are very small, just a couple of grams each. They are rough, unground, so I can test those.
I contacted a local college that has a great geology dept.-----am checking to see if they have specific gravity weighing equipment that goes out to 3 decimal places, and also if they have an XRF, so that I could verify the chemical composition, too.
Many, many thanks to y'all--------you've got me steered in the right direction to get these stones scientifically identified.
There was an anomaly when I was grinding the largest of these stones-----a tiny stone shaped like a triangular prism popped out of an 'outcrop', and it didn't look anything like the Carbonado-------------I've got to find that, and attempt to get a picture of it, and post that. I have no idea what it is, and it sure hit me as a strange ocurrence.
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Post by MsAli on Oct 19, 2018 14:22:16 GMT -5
Emerald?
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gemfeller
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Post by gemfeller on Oct 19, 2018 20:26:29 GMT -5
I can assure you that whatever they are, they're NOT alexandrite. Alex is transparent with the exception of the cat's-eye variant that contains parallel needle-like inclusions, making it either translucent or opaque with a chatoyant floating band (eye) in cut gems. I have some cat's-eye alex rough and it looks nothing like your stones.
I doubt it's carbonado (black diamond) because the stones look naturally stream-worn. It's possible but diamond's hardness would strongly resist that type of wear. A quick thermal conductivity test at your local jeweler's can determine if they're diamond. Many jewelers are trained in gem ID and have instruments like refractometers which would probably answer your question. You need a polished area to determine RI however. An accurate SG test would give you a place to start with ID.
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ampeg
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Post by ampeg on Oct 20, 2018 21:31:42 GMT -5
gemfeller, It took a whole lot of grinding with diamond discs to get them to the smoothness as seen in the picture------they were rough as cobs to begin with thanks for your info! I knew nothing about thermal conductivity testing for precious stones.
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hummingbirdstones2
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Post by hummingbirdstones2 on Oct 20, 2018 23:01:14 GMT -5
I think rocks2dust nailed the ID first. They look like some lower grade sapphires to me too.
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gemfeller
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Post by gemfeller on Oct 20, 2018 23:33:26 GMT -5
ampeg , natural diamond's thermal conductivity is about 5 times better than copper. Special detectors can separate diamond from other white natural stones as well as synthetics (other than syn. diamond) and other diamond simulants. As for your unknown being sapphire, possibly, but the rough shows no sign of hexagonal crystallization, though not all corundum occurs in identifiable crystals. I've also cut quite a bit of sapphire and while it grinds a bit slower than agates and jaspers it's fairly easy to shape on diamond wheels. While the Mohs scale shows only one number difference between the two, diamond is actually many times harder than corundum. After consulting my mineralogy books I think a careful hardness test would be sufficient to separate corundum from chrysoberyl and diamond.
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hummingbirdstones2
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Post by hummingbirdstones2 on Oct 21, 2018 10:00:26 GMT -5
Yep, testing is the only way to ID odd specimens with any certainty.
I haven't cut sapphire like Gemfeller has. Only suggested sapphire because I bought some sapphire "bombs" years ago. They were just ugly blobs, but I was buying specimens to learn how to ID things. If Gemfeller says the hardness test will be good enough, it will work.
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gemfeller
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Post by gemfeller on Oct 21, 2018 11:50:30 GMT -5
Yep, testing is the only way to ID odd specimens with any certainty.
I haven't cut sapphire like Gemfeller has. Only suggested sapphire because I bought some sapphire "bombs" years ago. They were just ugly blobs, but I was buying specimens to learn how to ID things. If Gemfeller says the hardness test will be good enough, it will work. Actually, it is the late and famed mineralogist Dr. Frederick H. Pough -- not me -- who suggests the hardness test as being determinative. His book "Rocks and Minerals" (Houghton Mifflin's Field Guide Series) is my go-to source on mineralogy questions. I should have credited him in my previous post.
The first sapphires I cut were star stones from Montana. I had only silicon carbide wheels in those days and it was a question whether I was cutting the wheels or the sapphires! I had to dress the wheels many times during the process because of the deep grooves worn in them by the sapphires. When I could afford to switch to all diamond equipment I was amazed at how easily diamond conquered the corundum. Diamonds are about twice as hard as corundum (again says Dr. Pough).
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hummingbirdstones2
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Post by hummingbirdstones2 on Oct 21, 2018 15:05:15 GMT -5
Yeah, Gemfeller, no matter who said it first we know you don't usually go off half-cocked.
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