[Jewelry making - Article 00076] - Re: [Orchid] Agatized dinosaur bones

[leonid surpin]

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>     But to really be termed an agate it needs to have the banded
>     structure of the fortification agates or brazilian agates. 

    The original post was correct, but simply vague. 

    Agates are classified into 2 large groups: Flat Parallel and Zonal
    Concentric. 

    What commonly called banded agate belongs to Flat Parallel and
    Brazilian agates are would be an example of Zonal Concentric. 

    About differences Agates and Jasper. 

    Agates form as a result of hydrothermal processes in igneous rocks,
    and only found in the shapes called Amygdales ( geodes ). It is
    interesting to note that in geology literature amethyst is called
    amethyst agate. 

    Jaspers form as a result of regional metamorphism, contact
    metamorphism, and hydro-thermal metasomatism. The later produces
    material which can be confused with agate, but in generally lacks
    agate structure. 

    So called moss agate is actually jasper with inclusions of chlorite. 

    The reasons why dino bones called agatized and not jasperized are
    related to difference in formative processes of these 2 minerals. 

Leonid Surpin
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