[Jewelry making - Article 00132] - [Orchid] GemBits - Jasper

[Sandra I. Smith]

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    The minerals grouped as jasper belong to the quartz family. Quartz
    is one of the most abundant minerals on Earth. It's formed primarily
    from silica and oxygen, but includes trace amounts of dozens of
    other minerals. Because of these mineralogical impurities, quartz is
    found in myriad forms. Mineralogists have divided the quartz family
    into two main groups: crystalline and cryptocrystalline.
    Cryptocrystalline is also called microcrystalline quartz. Due to its
    distinct crystal formation, crystalline quartz is usually
    transparent. Rock crystal, amethyst, citrine, and rose quartz are
    well-known examples of crystalline quartz. 

    The atoms in cryptocrystalline quartz pack together to form stones
    that are either opaque or translucent. The atoms take the form of
    fibers rather than crystals, and the stones often contain water or
    air trapped between the layers of fibers. 

    The cryptocrystalline quartzes are informally divided into two
    groups: jasper and chalcedony (kal-ced-nee). The jaspers are often
    opaque, while the chalcedonies tend to be transparent. Most
    mineralogists don't distinguish between the two, simply referring to
    both as cryptocrystalline. 

    Because there are too many cryptocrystalline quartzes to describe in
    one article, we'll use the commonly accepted groupings. The
    chalcedony family generally includes agate, aventurine, bloodstone,
    carnelian, chrysocolla and chrysoprase. Onyx, prase, sard, sardonyx
    and tiger's eye are usually classified as jaspers. 

    Although not now regarded as precious stones, the chalcedonies and
    jaspers were very highly valued in ancient times, not only for their
    beauty, but also for their reputed magical and medicinal properties. 

    Picture, or scenic, jasper gets its name from the pictures of
    scenes, animals or objects formed by the patterns in the stone. The
    unique markings are caused by fossilized algae trapped within the
    stone. 

    Ancient peoples used jasper to protect against pain, especially from
    childbirth. 

    Onyx is a catchall term used to describe several stones. The pure
    black stone often marketed as onyx is dyed chalcedony. The onyx used
    in architecture isn't a form of quartz at all, but rather belongs to
    the calcite family. Onyx agate is distinguished by parallel stripes.
    It's often used for cameos, and it's the mineral described in this
    article. 

    The stripes, or bands, on onyx are usually alternating black and
    white. When properly cut, the concentric bands look like eyes,
    leading most ancient peoples to use onyx to ward off the evil. 

    Although generally regarded as a protective stone, onyx gained a
    reputation as a stone of discord. It was never worn by lovers, nor
    was it worn at night, as it provoked nightmares. Prase, which means
    leek in Greek, is a pale green form of jasper. Prase is often
    included in the opal family, as one of the common opals. (Common
    opals lack the flash and fire precious opals are noted for. There's
    also a green stone recently discovered in Australia that has been
    named Imperial prase by its discoverers. They chose that name because
    it resembles chrysoprase. Their choice of name may or may not be
    recognized by mineralogists. 

    Sard is a reddish-orangish brown stone that was often paired with
    onyx by the ancients in the belief that the positive effects of red
    would dispel the negative aspects of the black onyx. 

    Sardonyx is very similar to onyx in that it has parallel stripes,
    and similar to sard in that the stripes are alternating
    reddish-brown and white. People wore sardonyx next to their hearts
    to heal depression. It was also thought to improve communication. 

    Tiger's eye starts life as crocidolite, an asbestos-like mineral.
    Over time, quartz replaces the crocidolite fibers, creating a
    silky-looking yellowish-brown gemstone. Tiger's eyes get their name
    from their chatoyancy. Chatoyancy refers to the appearance of an eye
    moving across the stone as it is rotated. The jasper family also
    includes petrified dinosaur bone and petrified wood. In both these
    instances, the original organic material was replaced by quartz.
    (This process is also called fossilization.) The replacement
    substance retains the same shape of the animal or plant. By its very
    nature, petrified material is ancient. 

    Turritella is very similar to petrified dinosaur bones, in that it's
    snail shells in which the original organic material has been
    replaced by quartz. It's found primarily in the state of Wyoming. 

    All the jaspers are cut into cabochons (rounded shapes) rather than
    faceted. Most are also made into beads or carved into ornamental
    objects. Like the other members of the quartz family, jaspers are
    found worldwide. 


****Sandra I. Smith, Writer ****






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