Imperial topaz, characteristics and description, from the Ouro Preto region of Minas Gerais, available in Teófilo Otoni

[Photo copyright of Anfilófio Bastos. Please click on the photo at left to see the full screen image in all its glory! Or, click on this text to go to a collection of photos of stunning examples of the finest imperial topaz from the region of Ouro Preto, Minas Gerais!]

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.

A great website for finding the technical data on minerals, and with many good photos of these minerals, is www.mindat.org

That site currently has over 50 photos of imperial topaz crystals of the various natural colors. The first, a light golden brandy in color, displays the typical size, shape, color, and form of the most commonly found imperial topaz crystal, not to mention the internal fractures. These crystals can be had for pennies, as they are not gem quality and are sold merely as curiosities. The descriptions of the imperial topaz crystals on mindat contain a lot of hype. Almost none of the brandy-colored crystals is gem quality. The lavender crystals, however, are valuable. Here is the link:

http://www.mindat.org/min-8110.html

Copyright © 2009 N. Tenney Naumer -- All rights reserved.

Here is a link to a flickr album with photos of variously colored imperial topazes cut and available at the firm of Duarte & Bastos in Teófilo Otoni (photos by Anfilófio Bastos):

http://www.flickr.com/photos/dbprecious/sets/72157622158501184/detail/