[Jewelry making - Article 01156] - Re: [Orchid] Andalucite? and general lab-creation question

[Renate Sommer]

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>           In the course of looking for interesting gems to set in my
>     jewelry pieces, I've run across Andalucite.  I'm not that familiar
>     with it, but it is very pretty, with interesting color and clarity. 

    Hi Karen I get the feeling that some people (as I have on occasion
    done) confuse Andalusite with Alexandrite. Vaguely similar names,
    both of the orthorhombic crystal systems and both with their own
    distinctive features. 

    My reference here is a little book called "Gemstones" by Cally Hall
    (a handy book with great photos and pretty accurate in its info I'm
    told) and I quote: "Andalusite varies in colour from a pale yellowish
    brown to a dark bottle-green, dark brown, or the most popular
    greenish red. It has very strong and distinctive pleochroism, so
    that, when turned, the same stone may appear yellow, green and red.
    Large crystals may be vertically striated prisms with a square
    cross-section and pyramidal ends, but are rare. More usual are
    opaque, rod-like aggregates of crystals or waterworn pebbles. It is
    the pebbles that are usually cut as gemstones." Occurences - "gem
    gravels of Sri Lanka and Brazil. Other localities include Spain,
    Canada, Russia, Australia and the USA." Hardness  is 7 1/2 

    There is no mention of rarity apart from that one crystal variety. 

    Alexandrite (which is a form of Chrysoberyl) on the other hand is
    "very rare and valuable" and "changes from green in daylight to red,
    mauve or brown under incandescent light, such as a light bulb.
    Synthetic chrysoberyl, synthetic corundum and synthetic spinel have
    all been produced to imitate alexandrite's colour change." In
    regards to occurrence it states "although mainly worked out, the
    best chrysoberyl, including alexandrite has been found in mica
    shists in the Urals (Russia)" 

    There's heaps more, but you may see from this the likelihood of
    possible confusion amongst your informants. 

    As to lab-created (synthetic) gemstones versus natural. Beauty is in
    the eye of the beholder. Actual brilliance must be the same in both
    as they are the same mineral, ie your Alexandrite is a Beryllium
    aluminium oxide and so is a synthetic Alexandrite, otherwise it is
    not a synthetic but rather an imitation. It is the minute little
    bits of other things that that make an alexandrite appear so
    different from a crysoberyl cat's eye (also Beryllium aluminium
    oxide). Refractive index is the same for both. Personally, although
    sparkly and pretty, the synthetic corundum imitating alexandrite is
    not a patch on the real thing. I had the good fortune to see one
    once. In natural light it was a deliceous deep blue green and under
    incandescent light an intense pinky purple. 

    All that gasbagging and you were asking about Andalusite. Hope the
    above was of some use though. 

    Renate from Adelaide, South Australia in the north of which state we
    find another form of Andalusite, call Chiastolite which are cigar
    like prisms which when cut in cross section have a cross-like pattern.

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