FMF - Friends of Minerals Forum, discussion and message board

[Luiz Menezes]

Alfredo:

We don't need to even read the name, for us the only thing needed on a specimen would be the locality; but the beginners need names. Based on scientific considerations we should abolish all names for varieties, so amethyst should be labelled only "quartz", everybody can look and see the color.
,
When we refer to a mine, a prospect, somebody else's specimen that is not in front of us, we should describe it: we can use "indicolite" or "greenish-blue elbaite", I prefer to keep using "indicolite".

Luiz

[Jason]

Alfredo, like many of my friends, is a purist and prefers the standard nomeclature..iie. zoisite(blue variety) instead of tanzanite. Once again thanks for the info Luiz..i wondered what aspect the crystal habit and form played in the arguement(argument meaning discussion and not arguing..:):):)) With imperials having smaller and less well defined euhdral faces. Now to throw another wrench into the discussion..another brazilian friend of mine has also been having this discussion with me on another forum at the same time..now she has brought this up to me before in the past and she, like you another brazilian, thinks the yellows and golds and oranges should also be called imperials. She also ads, i am not sure I agree with her on this but she also ads that imperials from ouro preto have. due to tiny micro flaws a quality that gives them a shimmer..I have seen the tiny interior flaws of an imperial and i know what she is speaking of. The discussion we are having on this other forum she now tells me that is the defining quality of a true imperial..the shimmer caused by the tiny micro inclusions/flaws.....I am going to copy the blog and post since last link i tried didn't get set up..think it was during Tuscon and Jordi and John were busy

"Recently, on one of the gemology forums, there was a discussion of imperial topaz. I was pretty surprised by the confusion as to what exactly is an imperial topaz.

For one thing, no one mentioned that the internal structure of real imperial topaz is quite different from common topaz. I don't have the technical vocabulary to describe it, but I can tell you what it does.

First, imperial topaz comes only from Minas Gerais in the region near the city of Ouro Preto. Minas Gerais is a very large state, comprising an area about 50% larger than the state of California, just to give you an idea.

The crystals are usually quite small in comparison to common topaz.

Unlike common topaz, their internal structure contains many tiny fractures. Thus, while cutting and polishing an imperial topaz, great care must be taken or it will break. And, sometimes these fractures are large enough to permit the polishing material to enter. Very fine visible fractures are normal in imperial topaz. Such fine fractures visible only at 10x normally do not affect the value of the stone greatly, although of course a really clear stone is more valuable, much like a clear rubilite tourmaline.

As already mentioned above, the crystal's color will intensify when viewed through the c-axis.

But the main difference is something called in Portuguese brilho de fogo, or "brilliance of fire."

Imperial topaz has a special way of reflecting light that causes it to shimmer.

Anyone who has actually seen real imperial topaz of even moderate quality will have seen this shimmer. It is somewhat similar to a schiller effect, but it is much finer and is extremely difficult to photograph, although I have come close even with my little amateur cameras.

Imperial topaz is defined by these special small shimmering crystals with internal fractures, and so far as I know, the only region in the world where they are found is in Minas Gerais.

As to color: imperial topaz comes in colors from a weak pale yellow to a better gold, to slightly orange, to salmon, to sherry and on along this sort of spectrum -- but they are all imperial topazes.

The difference is in the prices that are paid for these colors.

Some are heated to become pinkish. Lavender is a highly desired but rare color.

Nowadays, some are irradiated, but this is usually discernible because the colors have an intensity and tone that are not natural.

Generally, imperial topaz cannot be cut in the same way as common topaz due to the breakage problem. Thus, there are traditional cuts specific for imperial topaz.

I have seen irradiated citrines and low-quality rubilites cut in these imperial topaz cuts and hawked as imperial topaz.

Five years ago or more, common topaz (slightly off white in color) from the Khatlang province of Pakistan was being irradiated, and this process produced a very strong coppery orange shimmer, which unfortunately faded over time. It was noticeable that the shimmer effect was not nearly so fine. Nevertheless, these stones were often quite pretty.

The producers of this irradiated topaz did not bother to have it cut in the traditional cutting styles of real imperial topaz.

Very often, the irradiation produced very easily discernible color zoning -- something I have never seen in real imperial topaz.

The color was usually an orange copper with grey and brown undertones. It was especially easy to see these undertones and the color zoning if one put the stone, table down, on a piece of white paper and looked through the pavilion.

Sizes could go up to 40-50 carats -- an almost unheard of size for real imperial topaz.

But the dead giveaway was the price.

Even the lowliest cut imperial topaz with a washed-out, orange-salmon color (VS) would cost $12-$15 per carat in Teófilo Otoni."

[Luiz Menezes]

Amethystguy:

Your Brazilian friend has pointed out another feature that are common on the imperial topaz from Ouro Preto, Pakistan and Zambia/Congo: the tiny internal fractures that are never seen in topaz from pegmatites or rhyolites.

Luiz

[Jason]

Luiz..is that a defining quality for imperials or should you use color first and foremost?

[Luiz Menezes]

I don't think so; I am talking about imperial topaz crystals, not about cut stones. I would price at the highest rank the crystals with the combination of deeper reddish-orange to purple color and highest transparency.

Luiz

[Peter]

Indigolite is indigo blue tourmaline (elbaite most commonly)

Heliodor was "sun colored" beryl, now it beats why we would have needed this term when we already had golden beryl, but it is now widely used and accepted. In Finland one pegmatite produced some incredible gem quality green beryls and among them were some ture golden beryls or heliodores. I have preferred to use the term green beryl, as that was the color of the majority of crystals. In Volodarsk, Ukraine most bery crystals are yellowish/green and more rarelt pure green or pure golden heliodore, and in some cases also depending on light.

I agree with Luiz that the new african topaz shoule also be labeled Imperial. The color beeing the original criteria but from mineralogical and geological point of view of course the morphology and genesis. Most of the old Ural ones were found as noted in alluvial deposits but they are found in narrow quartzveins. A recent russian book "Russkaja Brazilia" Russian Brazil describes mineral deposits in this region of the Urals with photographs form the field, pits and the cover showing some newly found "Imperial topaz" crystals from the Urals in a suite of colors and nuances.

The irradiated Pakistani topaz crystals originally from pegmatites has nothing to do with Imperial topaz, Indeed they can attain a "synthetic" deep brown to orange color upon irradiation,

[Tenney Naumer]

Hi everybody! I thought I would stop by to mention that I am originally from Illinois, although I have lived in Brazil for the past 12 years.

[Tenney Naumer]

[Jason]

Hey Luiz..tenney is the one who told me about the shimmer i mentioned and you