I agree with Ronald Matheney's comment, but I have been out of the opal
field for some years, now, so may be work exists on precious opal I am
unaware of..
I or Anne Juillet Leclerc ([log in to unmask]) would be pleased to
give additionnal information
Laurent Labeyrie

>I don't believe there have been any studies of oxygen isotope ratios in
>precious opal.  I have analyzed biogenic opals (opal-A) as well as
>opal-CT and quartz chert; I have considered precious opals but never
>worked with them.  It is important to use an analytical procedure that
>eliminates the influence of the water component of opal, which can be
>quite large.  Reasonable methods are given by Labeyrie and Juillet (1982,
>Geochim et Cosmochim Acta vol. 46, p. 967-975) and by Matheney and Knauth
>(1989, GCA vol. 53, p. 3207-3214).
>
>You can contact me directly if I can be of any assistance.
>([log in to unmask])

----------------------------------------------------------
                   Laurent Labeyrie
         Professeur a l'Universite Paris-Sud Orsay
           Dept. des Sciences de la Terre
                        et
            Centre des  Faibles Radioactivites
                Laboratoire mixte CNRS CEA
            Domaine du CNRS, av. de la Terrasse
            F-91198 Gif/Yvette cedex  France
              tel 33 1 69 82 35 36
              fax 33 1 69 82 35 68

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