Hi, I was looking through an old parcel of stones I had from years back and I came across this stone, I believe that it's an Alexandrite, But I am not an expert. It weights about 1.5 cts and is almost flawless, It's almost hard to believe, thats why I am in need of help identifying. The color is greenish blue and is about 60-75% color change, cause it doesn't really turn pinkish purple until you hold a lighter or flame under it, the flash on the camera is the best to see the color change! Can anyone please help me, Below is a picture of the green color with no flash and the pink with the camera flash. Links to photo Below
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21600 Location: San Francisco
The ability to identify gems is neither simple, nor inexpensive. One cannot positively identify gems from looking at a picture. Optical tests are required and must be conducted by those with proper training and instruments.
Many stones appear to change color from greenish to reddish. They include, but are not limited to glass, fluorite, garnet, plagioclase (andesine/labradorite), synthetic sapphires, natural sapphires, synthetic alexandrite, natural alexandrite.
You need to have a professional gemologist optically test it for positive identification.
Barbra is right.. you cant do much from just a photo. However, you can gain some useful info by just playing around with it. Check out the most likely possibility, which is an "alexandrite" type synthetic corundum. Find amongst your collection of gems a known synthetic corundum and compare the optical properties. If you don't have a refractometer try comparing the optical properties when imersed in a liquid, such as cooking oil. My Helium article "How to identify a loose gemstone" may help at http://www.helium.com/items/2104650-gem-testing-today Cheers Allano
Hi!, guys thanks for all your help and feedback, I think I am going to heed all your advice and take it to a local certified gemologist or I am do a little more research and have it sent out to a lab and have a report done on it. Could anyone recommend a good lab to have gems certified? Thanks again for all your help.
Hi Jason It is good to see you taking an interest in an unknown faceted gemstone exhibiting a color change, which other than size, is about all the information available to guess what it is. It puzzles me why you suggest it might be a heat treated "andesine" presumably andesine feldspar, which is a material (gem) not even mentioned in Webster's book on Gems, but from his tables would have an RI of 1.55 to 1.56 & SG of 2.65, or values very close to quartz. Often the solution to a problem is the simplest. Obviously we need a value of RI to eliminate lots of possibilities ... is the RI low, medium or high, which is easily ascertained by immersion in cooking oil with other known gemstones. If the unknown is andesine, then it would give a shadow image the same as quartz, if of high RI it would exhibit an image like corundum. Very easy to do and costs nothing, but provides valuable information. Cheers Allano
Another interesting phenomenon displayed by this Mongolian feldspar is its tendency to scatter light off the copper nanoparticles that are responsible for the red and green color. If the stone is held next to a strong light source, the light will be scattered and give the appearance of a translucent reddish cloud with a well-defined pattern. The colorless and yellow areas show no scattering at all. The red areas show strong scattering, and the green areas show the strongest of all (figure 11). This feature is not visible in transmitted light, but is easily seen in oblique or strong top lighting, such as a tensor light or a fiber-optic light. This phenomenon is often confused with color change, in that a green stone may appear red in certain kinds of light (figure 12). The difference is that the colors are not dependent on the color temperature of the light (incandescent vs. daylight) but rather on the strength of the light source and the viewing angle
Full article: [pdfview]http://www.gia.edu/research-resources/news-from-research/identification-treated-feldspar.pdf[/pdfview]
Joined: Tue Aug 01, 2006 3:24 am Posts: 4997 Location: McDonough GA
allanotaylor wrote:
Hi Jason It is good to see you taking an interest in an unknown faceted gemstone exhibiting a color change, which other than size, is about all the information available to guess what it is. It puzzles me why you suggest it might be a heat treated "andesine" presumably andesine feldspar, which is a material (gem) not even mentioned in Webster's book on Gems, but from his tables would have an RI of 1.55 to 1.56 & SG of 2.65, or values very close to quartz. Often the solution to a problem is the simplest. Obviously we need a value of RI to eliminate lots of possibilities ... is the RI low, medium or high, which is easily ascertained by immersion in cooking oil with other known gemstones. If the unknown is andesine, then it would give a shadow image the same as quartz, if of high RI it would exhibit an image like corundum. Very easy to do and costs nothing, but provides valuable information. Cheers Allano
Hi Allano,
My reasoning is simple enough...I've handled hundreds of these cc copper diffused andesines. The photos are an exact match for the cc I have observed...as well as the tone of the green. Granted all of these are subjective and totally inconclusive...so my guess remains only a guess.
Hi Jason Thanks for all the up-to-date info on andesine which I was not aware of. Very interesting. My point of obtaining an approximate value of RI, very simply, would be a great help in determining what the gemstone is. Thank you once again. Allano
Hi Jason Thanks for all the up-to-date info on andesine which I was not aware of. Very interesting. My point of obtaining an approximate value of RI, very simply, would be a great help in determining what the gemstone is. Thank you once again. Allano
If you can get your hands on a copy of the latest edition of 'Gems' (Ed. M.O'Donoghue 2006), You will find a quite thorough treatment of the Plagioclase Feldspar series Albite-Anorthite. In particular, the details given in p 245-247 re. RI and SG are quite thought provoking I find.
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