[Jewelry making - Article 00017] - Re: [Orchid] Wood agate Vs. petrified wood

[Lee Einer]

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    We could certainly fine-tune the language where petrified wood is
    concerned. What we are really talking about is pseudomorphs after
    wood- with what is commonly referred to  as petrified wood, the
    original wood was covered with volcanic ash or other silica-rich
    material and the wood was replaced slowly by silica as the wood
    decayed, with the result that the patterns of the wood, the grain
    and in some cases the cell pattern, were preserved in the resulting
    pseudomorph. In other cases, the wood was buried in hot volcanic ash
    or lava, and the result was that the wood burned out, but left a
    cavity in the shape of the limb or twig, which later filled in with
    silica. In these latter cases, you have the shape of the wood
    preserved, but not the pattern. Most folks call this stuff a "limb
    cast," which, since it is a little like Mother natures investment
    casting, is not a bad term. Additionally, the silica which replaced
    the wood (or filled the cavity left by the wood) can be either
    cryptocrystalline quartz or opal. So really, we have four different
    stones falling under the general category of silicated wood
    replacements- agatized wood, opalized wood, and agate and opal limb
    casts. If you wish to consider chalcedony wood replacements as yet
    another separate category, things become more complicated. 

Lee Einer


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