[Jewelry making - Article 00359] - Re: [Orchid] The Beilby Layer

[Wayne Emery]

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Kevin,

    I've watched it many times on many species of stones....but Beilby's
    explanation included heat, a sort of melting at the point of
    contact. Doesn't happen. 

    What DOES happen with some materials, is plastic deformation of the
    surface. This has been confirmed again and again under the scanning
    electron microscope when preparing minerogical thin sections for
    viewing with a petrographic microscope. 

    As someone mentioned, there's a "flow" process, just not the way
    Beilby described. 

    Unfortunately, the resistance to plastic deformation is so high in
    many mineral materials that only mechanical disruption (abrasion)
    takes place. Scratch polishing. But some materials, when being
    polished with the oxides, react plastically and opal is one of them. 

Wayne
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