Gerry and All,
I have never seen a natural amethyst of sufficient size (about 1+
carats) that does not have tell-tale color zoning. It can be hard to
see, may require immersion, magnification, good lighting, & proper
color background - but it is always there from what I have seen.
Small stones may be impossible to to identify due to their size in
relation to the size of the color zoning.
IMO the frequently fluctuating natural environment causes the
numerous tell-tale color zones in the natural material. By contrast,
synthetic amethyst is grown fairly rapidly in a fairly constant
environment (big pressure cooker) which does not create the
conditions that cause the color zoning seen in the natural
counterpart. This will always be the case since nobody wants to
induce expense increasing solution, radiation, etcetera fluctuations
& wait around for 10 years or 100 years before pulling their
synthetics out of the auto-clave (pressure-cooker). That is what
Mother Nature does.
Besides this, if you have samples of the synthetic materials you can
see some of their tell-tale color zoning which is different in
character than the natural. The real problem in identifying natural
from synthetic amethyst lies in amethyst’s relatively low price. If
the effort costs more than the stone, even if the stone is natural,
it becomes… “uneconomical” .
Since amethyst specimens and crystals were my specialty (along with
cut stones) back in the old days - I took great interest in the
synthetics when they first appeared. The fact that Guerrero
amethyst was and still is the finest natural material IMO ever to be
mined, caused me great concern and reason to study the "new"
synthetics. The fine color synthetics definitely kicked the fine
natural stone market in the butt!
(Some of you may remember me from all the awesome Veracruz and
Guerrero amethyst specimens & crystals in Rm # 212 at the Tucson
Desert Inn. )
Regards, Steve Green - Rough and Ready Gems, Inc.
PS I will be traveling and out of touch for a few weeks. Also I
have had a hard time posting here lately. Three of them have not
appeared yet and it has been 3 days now.