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Tanzanite fake or real?


I have recently started gem collecting and have some questions
concerning tanzanite. I have heard tanzanite can not yet be grown in
a lab but yet I see lab tanzanite advertized all over the internet.
If so is there a way to tell the difference between lab created
tanzanite from the real deal just by looking at it with the naked
eye? Also, would a simulated tanzanite… lets say made of glass,
have the same red flashs, color change etc. as the real stone would?
Anyone with some insite on this subject?


I too am curious about tanzanite. A friend recently came back from a
trip to Alaska, and found that stores and the galleries in Juno,
Sitka, and other tourist places were flooded with tanzanite—some
at give-away prices They were all being sold as genuine. From the
amount being offered it would seem that there is no shortage of the
gem. She reported that some of the stones were huge-- 12X20mm and
larger. What is the story on tanzanite??


I do know a lot of people taking cruises far south to the islands are
being ripped off right and left… thinking there getting an
outstanding deal on tanzanite only to find when they get home they
end up with nothing more than a pretty piece of glass. After a lot of
research I’ve discovered that lab grown forsterite is being used to
create tanzanite that is very hard to detect as a fake but as far as
glass I wouldn’t think it could have all the natural characteristics
as the real deal… anyone with any thought on this subject?



As for your friend who made the trip to Alaska and found shops
selling a lot of Tanzanite, you would be safe in betting that they
were something else. They certainly weren’t Alaska products. Could
be anything. They would have to be tested to know for sure. I hope
she didn’t buy any. The tourist shops in southeast Alaska, Juneau,
Sitka, etc. are owned by the cruise ship companies which also
operate in the Caribbean, Mexico etc. etc. and wherever a tourist
dollar can be garnered. They sell the same crap everywhere they
operate. I’m sure many on this list have had clients bring in some
treasure they acquired in some exotic port which turned out to be
something other than represented… Caveat emptor!

Jerry in Kodiak (Alaska) Where we are untouched by Princess Cruises
et. al. :slight_smile:


Take a look under yttrium-aluminum garnet, hydrothermal corundum,
and czochralski pulled minerals.


but as far as glass I wouldn't think it could have all the natural
characteristics as the real deal.....

You’re right. Glass cannot have all the natural characteristics of
tanzanite, but how many people without any more training in gem
identification than they can get watching the shopping network are
capable of making the separation? I’m reminded of a story I heard
many years ago of a couple of Army pilots flying aC47 who landed at
some base in India. They had to remain there for a day or so and
they took some time off to do some shopping and sightseeing in the
nearby city. Being aware that India was known for precious stones
they were eager to take advantage of an obvious bargain when they
were approached by a local entrepeneur who offered them some
beautiful rubies, round, clear and well polished and at a really
attractive price… Returning to their aircraft, well pleased with
their purchase, they were beginning their runup prior to takeoff when
much to their shock and chagrin the noticed that all the little red
warning lights on the instrument panel were missing.! A little
knowledge is dangerous.

Jerry in Kodiak

After a lot of research I've discovered that lab grown forsterite
is being used to create tanzanite that is very hard to detect as a
fake but as far as glass I wouldn't think it could have all the
natural characteristics as the real deal..... anyone with any
thought on this subject? 

Hi All…

Most gem material one runs across is doubly refractive… Diamond,
garnet, CZ, and spinel are notable exceptions…there’s others, but
not so common…

So…a while back I got a frame to hold two sheets of polarized
plastic (aka Polaroid) in parallel to each other in the “crossed”
(darkest) position…about 3 inches apart…

When you stick a doubly refractive material in between the crossed
polarizers…and look at a light source… It lights up…and
blinks as you rotate it… A singly refractive material…like, say,
plastic or glass…will not… Even works for stuff like carnelian
and other translucent gem material pretty much…

Well, OK, there are some stress related anomalous conditions that
will cause the sorta the same effect with single refractives, but…

Nice Q&D (quick and dirty) test…

Uhhhh…dunno about forsterite…syn or otherwise…?

Maybe dichroscope…?

Gary W. Bourbonais
A.J.P. (GIA)


Related Articles:

Tanzanite - Zoisite - a Sorosilicate
By Edna B. Anthony

Tanzanite - A blue and purple beauty
By Arthur Anton Skuratowicz and Julie Nash

Gem Dealers’s Secrets - Handbook for the Gem Buyer
Zoisite: Tanzanite
By Sondra Francis


I don’t know about telling with the naked eye but have read that a
tanzanite stone will appear very slight red through a chelsea filter
whereas a YAG stone would be an intense red.

The other test to use would be to use a UV lamp and test both
longwave and shortwave ( if I remember right, Tanzanite does not
flouresce). I’ll double check on what shows what and post again. I
think a Forsterite stone would show no fluorescence under longwave
but will show muddy green or yellow under shortwave.

So far I’m unaware of lab-grown tanzanite being on the market but
would appreciate a heads up if anyone out there knows otherwise.

I bought some stones recently but am curious to know what the rate
is around the world for stones around 1.5 to 2 carat. I’d like to buy
more and would like some indication of what I should be paying. Oh,
there’s now Tanzanite foundation certified stones.

Some info here


I do know there are a set of filters you can use to help determine
if they are real and as a matter of fact I beleive there is one to
distinguish tanzanite from forsterite too! While I’m on the subject,
think I’ll just pop right on over to that site and purchase them
right now! If these stone are the real deal and by the looks of them
I think they are I absolutly lucked out like you wouldent believe! :slight_smile:
If they pass the filter test I’ll then take a couple to a gemologist
and have them positivly identified. Keep me posted on any info you
learn and in return if indeed they are the real deal I’ll share my
lttle source if your interested in investing in more!

The tourist shops in southeast Alaska, Juneau, Sitka, etc. are
owned by the cruise ship companies... 

It’s true, the situation here in Juneau has gotten and is getting
worse every year. May I say that not every store is controlled by
the cruise ship companies. I work for a store that is locally owned
and staffed year round by Juneau residents who love Alaska and more
importantly love fine jewelry and gems. We are not bought or sold by
Princess or any other Caribbean conglomerate. To anyone who visits
southeast Alaska by any means, please come into Fire & Ice. We are
the real thing. Gem and Jewelry junkies with an Alaska problem…

-BK in AK

    would a simulated tanzanite... lets say made of glass, have the
same red flashs, color change etc. as the real stone would? Anyone
with some insite on this subject?

Hi Sheila,

It’s true that tanzanite has not been synthesized in a laboratory
and, as you’ve certainly read on this forum, there are a few
imitations. I wish there were a simple layman’s answer for you but
the truth is that it is difficult to separate some of these
materials without at least some basic gemological training and

For instance, zoisite (tanzanite is the blue variety of zoisite) has
a refractive index of 1.69 to 1.70, a biaxial positive optic
character, specific gravity of 3.35, birefringence of.008 -.013 and
is generally inert under longwave ultraviolet light. This is the
basic info you need to separate it from its’imitations.

Coranite is a trade name for one tanzanite imitation. It is a
purplish blue synthetic corundum with a typical RI of 1.762 - 1.770
and a birefringence of 0.008. Its optic character is uniaxial
negative, which is quite different from tanzanite and it is inert to
UV light.

Some manufacturers have created a bluish-purple yttrium aluminum
garnet (YAG) that looks a lot like tanzanite called Tanavyte. It is
singly refractive with an RI of 1.80, which is over the limits of
most gemological refractometers. Even so, it may show anomalous
double refraction in the polariscope due to strain in the crystal,
but that also means there is no birefringence or pleochroism.

U.M. Tanzanic is leaded glass with an RI of around 1.60, and also
singly refractive. Tanzation is a synthetic spinel triplet with a
fused cobalt layer. RI is 1.72 and it’s also singly refractive, so
no birefringence or pleochroism.

You’ve doubtless read about the synthetic forsterite here, and it is
definitely the most difficult tanzanite imitation to separate, even
though it is most closely related to peridot than to zoisite. It’s
optic character is biaxial positive like tanzanite, but it’s RI is
significantly lower at 1.64 - 1.67. That also means it’s
birefringence is much higher at.035. It is strongly pleochroic like
tanzanite, but only shows two colors through the dichroscope,
whereas tanzanite displays three colors. Earlier, I mentioned that
tanzanite is inert to ultraviolet light, but synthetic forsterite
often fluoresces a weak, chalky orangy yellow when exposed to
long-wave ultraviolet radiation and a weak greenish yellow to
short-wave UV.

Sheila, as a person who has recently started collecting gems, I don’t
expect you to be able to take the kinds of readings or even own the
equipment necessary to make the separations required of a gemologist.
What I am attempting to do is get people to understand how easy it
can be to get ripped off by unscrupulous dealers, or even ignorant
ones. Internet sites and legitimate gem dealers often have no idea
that they themselves have been hoodwinked into buying imitations or
synthetics before they resell them to the public. I guess what I’m
saying is that you should find yourself some reputable dealers,
wholesalers, retailers, etc., who you may buy from with confidence.

All of the above is a long, unnecessary narrative to answer the
question of whether there is a way to tell with the naked eye if a
gemstone is tanzanite or one of its’imitations. Apart from some
batches that “just don’t look quite right” the answer is:

Nope, sorry :frowning:

James S. Duncan, G.G.
James in SoFL