[Jewelry making - Article 00530] - [Orchid] Imperial vs Common Topaz

[Steve Green]

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    The Topaz from Ouro Preto Brazil (imperial topaz) is slightly
    different mineralogically and chemically than topaz from other
    worldwide localities.  It's crystal habit, color stability &
    coloration differ from the more ordinary topaz. 

    Most topazes are very light sensitive and fade in direct sunlight.
    The Ouro Preto imperial topaz as a general rule does not. Imperial 
    from Ouro Preto also has a unique pure orange to red to fuchsia
    coloration devoid of the brown, gray and bluish-green tones so
    commonly found from nearly all other locations. The crystal habit of
    imperial topaz shows a longer c-axis in relation to the A & B axis
    than other locales and also has striated prism faces while other
    locales do not. Somewhere in the past I read in a credible source
    that the actual chemical & physical properties of the Ouro Preto
    topaz is different than other localities. Something to do with the
    hydroxyl group (OH) and the pH during formation if I remember
    correctly, and slight differences in RI and SG. 

    Anyone who is familiar with the Ouro Preto rough or crystals will
    immediately recognize this locale  by very apparent and unique
    properties. It almost looks like a different mineral species when
    compared to common topaz. As I type this - I have in front of me a
    Thomas Range Utah crystal, a San Luis Potosi, Mexico crystal (often
    erroneously referred to as Guerrero), a Tarryall Colorado crystal
    and Ouro Preto imperial crystal.  The first 3 materials all have
    many similarities in their crystal habit that the Ouro Preto
    Imperial material does not share. Hard to sum up in words, but very
    apparent in person. 

    Even amongst the material from the Ouro Preto area there are very
    specific mines each with its own and unique attributes. 

    Here are a few: 

    a.. The Rodrigo Silva mine produces natural super colors approaching
    fuchsia-magenta. 

    b.. Antonio Pereira produces large very orange with little dichroism
    in the crystals. 

    c.. Vermelao ( I forget the exact spelling but the town behind the
    old bauxite smelter) produces huge up to brick size salmon red-pink
    colored crystals. 

    d.. And there are other mines around Ouro Preto that produce their
    own unique varieties. 

    Pakistan produces the  material most similar to imperial topaz from
    Ouro Preto.  It approximates the color of some of the Brazilian
    material but not the best. Overall the Pakistani size and quality
    does not come close to what Ouro Preto has produced. I am not sure
    if it is color stable in strong sunlight or qualifies to be called
    imperial topaz. Of course the Pakistani dealers all call it
    imperial. 

    Anyways what I stated above is based on my visits to Ouro Preto and
    dealings with the material and mine owners. My knowledge of the
    Pakistani material is from shows and written materials. A lot of my
    topaz knowledge is from my years spent in the mineral business
    seeing specimens from many locales, talking with mine owners and
    Brazilian dealers. The largest and one of the most prolific mines in
    Ouro Preto is actually owned by and American mineral collector who
    is quite wealthy and keeps all in his private collection. And what a
    collection it is. Sometimes he puts it on display in Tucson at the
    Main Show. Maybe you've seen it?   Hope this helps somewhat. 

    Steve Green / Rough and Ready Gems, Inc.   www.briolettes.com 



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