identifying synthetic amethyst

[tbar]

I am a G.G. and wonder if anyone has a simple tool to identify synthetic amethyst.  I have read that synthetic amethyst is NOT pleochroic whereas natural amethyst is.  I have tested a sample of synthetic and natural amethyst and this test seemed useful in separating the two.

[Richard Sherwood, GG]

Hi Tbar.  I've heard that the AIGS lab in Bangkok under Ken Scarrat's directorship developed a "simple" test to differentiate synthetic amethyst.  I've heard that the AGTA lab is also working to develop this test, but to my knowledge the method has yet to be shared with the rest of the gemological community.

In the meantime the characteristics I'm familiar with in identifying synthetic amethyst are:

1.  Bread crumb inclusions (characteristic of hydro-thermal growth, visible under high magnification)
2.  Nail head spicules (characteristic of hydro-thermal growth, visible under high magnification)
3.  No color zoning, or different shades of purple color zoning, versus the purple/white or purple/blue color zoning of natural amethyst.
4.  Lack of Brazil law twinning (although a minority of hydro-thermally grown crystals have this twinning induced)

Usually natural amethyst (being a GIA type 2 category stone, which usually crystallizes with slight inclusions) has inclusions which will allow you to immediately identify them as natural under a microscopic.  The synthetics are usually near flawless, and can usually be determined with the above four characteristics.  I wouldn't call it a simple process though.  

I haven't heard about synthetic amethyst having a lack of pleochrism.  I don't understand why that would be so.  I'd love to read your source on that info if you have it handy, as well as hear about your experience regarding it.

[opalmaster]

Hi Tbar:
Try to find the article by Bob Crowningshield for pretty reliable ident through the use of a regular polarizing filter.
Check the archives at: http://gia.metapress.com/content/h236m7p7743233h7/

Best of luck, and good hunting.

Gerry Manning

[Cara]

I agree that pleochroism shouldn't differ between the natural and synthetic. Seeing the interference colors in the polarizers due to twinning is the quickest, most simple method - but not 100% reliable by any means. If we rely on it too much, they will grow more twinned synthetics. Becoming familiar with natural and synthetic inclusions is better.

In our lab, we use FTIR. I don't find this method fast, nor conducive to more than one stone at a time. It would be interesting to see how GIA does this. Sometimes labs will keep methods quiet if by revealing the test, synthetic growers will learn to get around it.

Natural Quartz varies so much, it is not unusual to see something so odd you think it must be synthetic - but it's not.

Cara Williams