Unheated tanzanite?

[jstarfireb]

Anyone here have some info on unheated tanzanite? I was told that almost all of the blue/violet tanzanite out there is heated, but I hear occasional info on unheated tanzanites of this color. I understand most unheated tanzanite is brownish, not bluish. Has anyone seen an unheated blue/violet tanzanite in person? Do they have a characteristic color or appearance?

Thinking of buying one that I''m told is unheated, but I''d like to know more about the subject before I commit.

 

[serenitydiamonds]

Date: 10/26/2009 8:58:32 PM
Author:jstarfireb
Anyone here have some info on unheated tanzanite? I was told that almost all of the blue/violet tanzanite out there is heated, but I hear occasional info on unheated tanzanites of this color. I understand most unheated tanzanite is brownish, not bluish. Has anyone seen an unheated blue/violet tanzanite in person? Do they have a characteristic color or appearance?


Thinking of buying one that I''m told is unheated, but I''d like to know more about the subject before I commit.

It is extremely, extremely, extremely rare, and unlikely to find tanzanite rough in gem quality colors without heating. Almost 99.5% is heat treated prior to cutting. Tanzanite is usually brownish before heating, blue and purple after. For something that claims to be unheated, I strongly recommend a lab report.

--Joshua

 

[Indylady]

I think that MTG has one from Gene.

 

[morecarats]

Unheated tanzanite is much rarer than unheated sapphire (but not as rare as unheated blue zircon). A certified unheated blue tanzanite would be worth a lot. But it would be very risky to buy one without a cert.

 

[Swala Gem Traders]

jstarfireb,

The only reason to heat a zoisite (tanzanite''s name for the mineral) is if the initial color (whatever the color) is not judged attractive.

Although most zoisites are expected to be sold as blue tanzanites (because that''s where the market is) there are fancy zoisites which can, on rare occasions, be very attractive, prior to heating.
Therefore, there are two main reasons reasons NOT to heat a zoisite:
. the color blue is nice as such and does not need any enhancement
. the color, not blue, is judged attractive, and will be sold as a fancy zoisite (yellow, green, orange, pink)

Keep in mind that a huge percentage (significantly above 99%) of all zoisites are heated.

Few labs will give you accurate results regarding the heating of zoisites (I tested one known lab a few years ago and they gave me an inaccurate result - the gem was purchase by us as rough, was cut in our workshop and was never heated).

I hope this helps.

 

[MakingTheGrade]

Yup, I have an unheated tanzanite from Gene that's a lovely violet with a touch of grey. No certification, but I trust Gene since he goes to Tanzania to get his own rough and usually heats it himself. There's also an inclusion in the stone that would make me think that nobody would have tried to heat it lest it crack the entire thing.

But I could be wrong. It wouldn't be a huge deal though since I still love how it looks, and I hadn't paid a premium for it's unheated status.

 

[morecarats]

Date: 10/27/2009 5:44:50 AM
Author: Swala
jstarfireb,

The only reason to heat a zoisite (tanzanite''s name for the mineral) is if the initial color (whatever the color) is not judged attractive.

Although most zoisites are expected to be sold as blue tanzanites (because that''s where the market is) there are fancy zoisites which can, on rare occasions, be very attractive, prior to heating.
Therefore, there are two main reasons reasons NOT to heat a zoisite:
. the color blue is nice as such and does not need any enhancement
. the color, not blue, is judged attractive, and will be sold as a fancy zoisite (yellow, green, orange, pink)

Keep in mind that a huge percentage (significantly above 99%) of all zoisites are heated.

Few labs will give you accurate results regarding the heating of zoisites (I tested one known lab a few years ago and they gave me an inaccurate result - the gem was purchase by us as rough, was cut in our workshop and was never heated).

I hope this helps.

There is an interesting article about mining in Madagascar by Vincent Pardieu that was in Colored Stone a few years ago. Here''s a relevant passage from the article:

"But the Ilakaka gem market is not an easy place to buy and make money. Buying gems is simple; making a profit is a challenge. There are many risks, and it seems the closer you get to the mines, the more scams you find. Sapphires that are heated locally at low temperature to improve their color are commonly sold as unheated gemstones. Gemstones are routinely “improved” with ink and added to parcels. Sapphire rough that was heated abroad (and turned out badly) is brought back to Ilakaka to be sold again locally as unheated rough. You will also find broken and tumbled synthetics that look like natural, alluvial crystals; irradiated yellow and orange gemstones which will fade with time; and, of course, the traditional glass and imitation gemstones that are a mainstay of gemstone markets all over the world."

I''ve had many an honest and well-intentioned dealer say to me, "I know it''s unheated, I cut it from the rough myself." The fact is a lot of rough stone is treated before its cut. The only way to know for sure is to have it tested at the best gemological lab you can find. When you hear "the labs can''t test this," the red flag should go up.

 

[Swala Gem Traders]

Vincent has spent the past two weeks visiting us in Tanzania and is now travelling with my brother to Mozambique. His experience of the field is great. What he says is absolutely correct. Being at the source, we experience this very often. A lot of synthetics, imitation and fakes are found in producing countries. Nothing however beats local knowledge (knowing the deposit, knowing the miners/brokers, speaking the language etc).
Each find, each deposit, each gem is to be considered differently. In some cases, synthetics can be produced (spinels, rubies for instance), in other cases imitations (forsterites vs tanzanites), with garnets imitations/treatments are not easy to produce etc...
There''s no real premium for unheated tanzanites. In other words, miners/brokers will never pretend that the rough is unheated. It''s just not much of an argument. When you purchase a parcel of rough tanzanites, you''ll find pieces of different colors (trichroic gem) and may find a nice piece of natural blue rough. Tone/saturation are much more important than the fact that the zoisite is naturally blue (on the other hand, a nice naturally pink zoisite will be sold as such).
Moreover, tanzanites are usually heated once cut. As MakingTheGrade points out, tanzanites are heated either after the pre-shape or after the entire cutting is done. One tries to get rid of the natural inclusions before heating. Inclusions are generally of a different chemical nature in tanzanite which will, under heating conditions, react differently than the zoisite. The gem may break if heated with an inclusion inside.
In the case I am referring to, the tanzanite was of a natural blue. The lab I sent the gem to tested the gem in 3 different places. Two came out as being "unheated" and the third as "heated"...
I''m not saying labs can''t test an unheated tanzanite, I''m saying that they would have to work on a method. Some labs have, some haven''t. The reason why they haven''t is precisely because there''s not much of an economic reason to spend too much time on such method; as there''s not much demand to determine if a tanzanite has been heated, hence the absence of real premium for unheated tanzanite...

 

[MakingTheGrade]

Thanks for the information Swala! Very informative.

I''m glad there isn''t a market demand for unheated tanzanites, otherwise I might not have gotten to buy the one I did. I mostly bought it unheated because I have a personal preference towards stones that aren''t heated or treated. Not because it''s more "valuable" from a economic standpoint. Which is also part of the reason I didn''t bother to get it certified. Not only do I have a lot of trust in Gene and his experience, but being unheated doesn''t seem to affect price, so aside from assuaging my personal curiosity, it wouldn''t have affected the monetary value of the gem.

It''s the one in my avatar currently, I''m hoping to get it back by Christmas

 

[PrecisionGem]

While I was in Tanzania, a miner brought in some rough tanzanite, out of about 50 pieces, there were 3 or 4 that were blues and or purples. The rest was material that could heat. So why would he have heated just a few? That wouldn''t make sense, plus as Eric mentioned, the stones are almost always heated after cutting.

 

[jstarfireb]

Very interesting - thanks for all the info!

I was mainly looking at unheated stones because I have quite a bit of heated ones and kinda wanted something different. This is the stone in question, described as ".79ct natural, untreated oval tanzanite, measuring 6.93mm x 5mm." The seller who purchased the rough and cut it is well regarded here. No treatment was disclosed to him when he bought the rough.

He said this: "I bought the rough uncut gem years ago and cut it myself. Tanzanite is usually treated after cutting is completed because it does not need an awfull lot of heat to darken the color. If this gem was heated it would be darker blue violet. Sapphire is generally heated to near its melting pointing point to clean up the clarity and change the color. Tanzanite only needs to be heated at about 300 degrees in order to deepen or change the color. Hope this clears up any doubts."

Does this look like it might be a truly unheated stone? It''s small and inexpensive so I''m inclined to go for it...

 

[jstarfireb]

Actually I just realized that I put the wrong picture over the "most true to life" statement - it''s actually the top RIGHT that is most true to life.

 

[LD]

I would agree that there is no premium associated with unheated Tanzanite (if it''s the "normal" colour of blue). However, you can get unheated Tanzanites in colours other than blue and these are more difficult to find. Here are some of mine and they''re green, pink and yellow.

 

[jstarfireb]

Wow LD, your collection never ceases to amaze me! I''m a green person and would love to have a green tanzanite.

I''m inclined to believe it''s true that the one in question is unheated. Here is another tanzanite from another vendor, described as unheated, and of similar color...

 

[LD]

jstar - thank you for the compliment.

Typically unheated blue Tanzanite will either have grey or brown tones and in the photos you''ve posted I can definitely see grey so I would think it is unheated. HOWEVER, the price, when you''re considering Tanzanite, has no bearing on its heated/unheated status and it''s all about colour, cut and clarity. Sooooooooo, if you like the cooler tones of an unheated Tanzanite it is actually at the cheaper end of what you''d expect to pay. As a ballpark figure, Tanzanites of that colour are probably only around the $300 per carat mark (quite often less than that). I hope that helps?

 

[StonieGrl]

I have seen unheated tanzanite for sale by Pala International and they have a good tutorial on tanzanite on their left side education hyperlinks (good tutorial on most gemstones including price ranges, last time I saw it).