[Jewelry making - Article 00449] - Re: [Orchid] Gemstones Treatments

[r_carew]

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James,

    Too true, everybody is convinced that the only true black is from
    Lightning Ridge.  There are many other black base colored opals.  The
    opal I mined here in Arizona in the early 90s had some black potch
    mixed in with the blue body color.  I am seeing some good looking
    dark crystal from Coober Pedy too, although I don't know how stable
    it is, having heard conflicting reports.  There is of course the
    Virgin Valley black opal that none can deny has gem quality play of
    color.  It is quite beautiful if kept in water.  I have one small
    piece that I got at Keith Hodson's store here in Scottsdale that I
    cut and polished over 12 years ago and it is still stable.  Most is
    not.  The opal you are showing is not what I would call "gem
    quality" although pictures are not always a good way to judge quality
    of opal.  I will be honest with you and say that if you have ever
    held a true gem quality black opal in your hand and watched the play
    of color shift and change as you move it you will never mistake a
    Lightning Ridge opal for any other.  After long familiarity one can
    even tell which field it came from. 

    The only opal I have ever seen that is comparable is the opal coming
    out of a small state in Brazil.  I will be getting about 1.5kg of
    opal from this area in Brazil in a couple of weeks and will post
    pictures of the parcel on my web site.  I am still in the creation
    part of the web site so will post an address when it is ready to go. 

    I am told that they are also finding black opal in that area of
    Brazil, which is one of the only other areas in the world where opal
    is found in a sedimentary formation.  The sedimentary opal in Brazil
    is very much like the opal in Australia, except I am told it is
    harder and so makes a better gemstone. 

    Even the 'boulder opal' is in sedimentary rock.  It is found in a
    Precambrian metamorphic granite which has opal formations thought to
    be of the Jurassic-Cretaceous period and during the time of the
    creation of the south Atlantic the sedimentary rock was put under
    tremendous pressure and became a metamorphic type of granite called
    schist.  Without having inspected the surrounding geology myself I
    must rely on a paper published (in English) by a geologist from the
    University of Sao Palo. 



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