alan
starting to spend too much on rocks
Member since December 2013
Posts: 111 
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Post by alan on Dec 18, 2014 13:47:39 GMT -5
I dont have a picture, but my wife's mother came back from China with a stone that had been given to her many years ago... It does have color changing properties and changes from an amethyst like purple (indoors) to green (outdoors). I used my Presidium gem tester (Thermal conductivity) to see where the stone registered, and it registered on the low end of sapphire and middle for the topaz reading. The only thing that keeps me from thinking this is natural alexandrite is the size and clarity of the stone... it is 12x14mm oval and is eye clean...
Any ideas?
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on Dec 18, 2014 16:13:09 GMT -5
Most stones of that description coming from china are indeed sapphire with color change properties. If it was native alex that size very few people could afford it and eye clean?? lol No that isn't native alexandrite.
I cannot tell where you are from, but I have some known USA made syn-Alex cuit stones you can put in your machine. Mine are x-laser material. If you are local to me we could meet up and test mine on your machine.
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Post by gingerkid on Dec 18, 2014 19:04:57 GMT -5
Might be synthetic corundum or spinel? Hope gemfeller will see your post. |
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gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,062
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Post by gemfeller on Dec 20, 2014 14:38:54 GMT -5
Your stone is almost certainly synthetic corundum (sapphire) doped with vanadium to induce color change somewhat similar to alexandrite. Your natural skepticism about size and clarity is right on the money. A genuine alex that size and quality would be worth many tens of thousand of dollars, maybe millions. I recently sold a very small natural alex from India to a gemologist for $3,000/ct. and it didn't have top color-change or clarity.
The synthetic sapphire sold as alexandrite is made by several processes. Most is produced by the flame-fusion method invented by August Verneuil in the 1890s. Since then large synthetic sapphires posing as "alexandrites" have been sold to tourists around the world. True synthetic (man-made, chemically identical to natural) alex was first manufactured in California in the 1980s. There's a possibility your stone could be that material but it would have cost several hundred dollars.
A simple test is to have a gemologist check the refractive index. The synthetic sapphire will test as sapphire, not chrysoberyl (alex). If it tests as chrysoberyl then it would be time for more exhaustive tests but it will almost certainly be found to be man-made. Fine natural alex is awesomely rare and expensive.
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on Dec 21, 2014 14:52:55 GMT -5
Your stone is almost certainly synthetic corundum (sapphire) doped with vanadium to induce color change somewhat similar to alexandrite. Your natural skepticism about size and clarity is right on the money. A genuine alex that size and quality would be worth many tens of thousand of dollars, maybe millions. I recently sold a very small natural alex from India to a gemologist for $3,000/ct. and it didn't have top color-change or clarity. The synthetic sapphire sold as alexandrite is made by several processes. Most is produced by the flame-fusion method invented by August Verneuil in the 1890s. Since then large synthetic sapphires posing as "alexandrites" have been sold to tourists around the world. True synthetic (man-made, chemically identical to natural) alex was first manufactured in California in the 1980s. There's a possibility your stone could be that material but it would have cost several hundred dollars. A simple test is to have a gemologist check the refractive index. The synthetic sapphire will test as sapphire, not chrysoberyl (alex). If it tests as chrysoberyl then it would be time for more exhaustive tests but it will almost certainly be found to be man-made. Fine natural alex is awesomely rare and expensive. Nice Rick! I should add that my man made laser alex in cut form sells for about $150-$300 per carat - wholesale. |
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Post by rockjunquie on Dec 21, 2014 17:00:54 GMT -5
I remember not so long ago, at a gem show, a big colorful stone that I fell in love with. The seller graciously allowed me to take it outside the building to see it in daylight. I thought - what a trusting man! When I came back in, still drooling over the stone, he told me what it was and its true worth. It was a lab corundum "color change alex". All of a sudden I felt much less privileged and quite embarrassed that that I thought that he had trusted me with an Alex. LOL!!! Pretty as it was- I passed.
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