[Jewelry making - Article 01423] - Re: [Orchid] Flintstone arrow head

[Richard Davies]

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>     Check it for cracks of any kind since flint is schist it flakes it
>     should be a combination of flint,quartz and sometimes even tuffa
>     since these can stand considerable heat using normal wet wadding
>     and cooling techniques should work. 

    Just to clarify a couple of points- 

    Flint technically is the form of cryptocrystalline quartz found in
    the Cretaceous chalk formations of southern England. The name has
    been loosely applied to somewhat similar quartzes (cherts, jaspers,
    and chalcedony, for example) found elsewhere around the world, and
    often used in making the tools and points so useful as markers of
    various prehistoric cultures. 

    Schist, on the other hand, is a high pressure metamorphic rock
    consisting of micas, quartz, garnet, and various accessory minerals,
    depending on the chemistry of the original rock and the proximity of
    other mineralizing bodies. It is unlikely that a low temperature
    quartz like flint will be found within a schist, unless near-surface
    hydrothermal processes have emplaced that form of quartz in cavities
    in schist. (I have personally found banded agate in cavities in vein
    quartz eroded out of schist or phyllite.) 

    Tufa is a general name for surface deposits of calcium carbonate
    left as a result of spring activity, especially near limestone
    bedrock. It sometimes encloses plant materials. Travertine is
    actually a bedded form of tufa used as an ornamental rock similar to
    limestone or marble. The name is also sometimes erroneously applied
    to the eruptive volcanic rock rock known as tuff, essentially a
    solidified pyroclastic flow. 

    With respect to the application of heat, modern flint knappers
    sometimes use heat to make their raw material more brittle and
    easier to flake. Any cryptocrystalline quartz is somewhat porous, and
    might contain enough water to cause fracturing if heated enough. So
    care is necessary if using a torch in its vicinity. Heating is
    deliberately used to make carnelian redder, so it is certainly
    possible to heat these materials without destroying them. 

-Dick Davies
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