Sunday, March 29, 2009
How To Tell If Tanzanite Has Been Heated
According to my new book, Gemstone Identification Made Easy, there is a fairly simple way to tell if your Tanzanite is natural in color, or has been heat treated. Most Tanzanite comes out of the ground, brown or green color, and then is heat treated to get the various bluish purple colored gemstones. However some Tanzanite comes out of the ground those colors, naturally. Of course these gemstones would have a much greater value, than the heated variety. Plus you may be being charged too much for a stone being sold as natural, when in fact it has been heat treated. The use of a dichroscope, can help you in determining if your stone has been treated or not. Tanzanite is a trichoic gemstone, meaning it shows three different distinct colors. When looking through a dichroscope, you will see three distint different colors. Natural, unheated Tanzanite will show blue, purple, and green. Sometimes the purple color will be reddish, and sometimes yellow instead of green. However the important thing is that you will three distinctive different colors in unheated Tanzanite. The green, yellow coloring is very often not seen in heated Tanzanite. If you view through your dichroscope your Tanzanite, and you see blue, purple, and green chances are good that you have gotten an unheated, natural Tanzanite. Congrats to you, if you have such a rare, and fabulously valuable Tanzanite in your collection.
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4 comments:
This is very interesting and useful info. I had never heard of this method before. Thanks for sharing :)
You are welcome, thank you for stopping by.
Never heard of a "dichroscope." But I understand that real unheated tanzanite will look blue on one face and purple on the perpendicular face. Some is also TRIchroic where, if you turn it perpendicular to the other two faces (the "z axis") is will look reddish. Heating supposedly destroys this trichroism (and dichroism). 99% of tanzanite is said to be heat-treated and most sold as unheated is actually heated.
Finding a natural blue tanzanite is very very rare. TRUE "D" block tanzanites from surface are extremely rare and it is proposed that an ancient forest fire is what heated those surface stones making them blue.(They are concidered mined out). It is acceptable practice to heat a tanz and any deep blue gem can be assumed. There are still"D" blocks from below surface mined today. So don't be fooled. When buying any gemstone. Unheated Taz are as described above and generally in nature a dull ugly brown stone. Be educated and for a few $100 you can buy some relatively good /cheap equipment to help you out. know the mineralogy it can be found all over the web. Beware of GIA/ EGI certs as they'll cert anything for anyone willing to pay the fee. So that security blanket is gone by the greed side.
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