[Jewelry making - Article 00575] - Re: [Orchid] Tuffa and cuttle fish casting

[Orville & Rose Alene]

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    I think there has been a clarification on the use of the words tuff
    and tuffa since Lyell's book, at least in English.  I am looking at
    the "Dictionary of Geological Terms", third edition prepared by the
    American Geological Institute.  In here tuff is listed as a "general
    term for all consolidated pyroclastic (yes, of igneous origin) rocks,
    Not to be confused with tufa. (possibly the Italians still label both
    as tufa) But tufa in this dictionary is a chemical sedimentary rock
    composed of calcium carbonate.  In other words, the stuff found
    encrusted around hot springs and such.  A hard, dense variety of it
    would be called travertine.  Of course, the igneous (volcanic) one is
    the one we want for casting. Hope this helps. Rose Alene McArthur 

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