[Jewelry making - Article 00454] - Re: [Orchid] Using the term semi precious gems

[Wayne Emery]

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Leonid,

    Again, you are correct about the beryls in general and emerald in
    particular. The hydrothermally grown material is noticeably tougher
    and harder than the natural, and the natural material, if "clean" is
    pretty sturdy. Although, as noted by someone else, emerald is always
    more brittle (less tough) than aquamarine. I don't readily detect
    much difference between synthetic aqua and natural, but I think I
    read somewhere that the hardness of aqua rises with increasing RI in
    the material as noted from different localities. Maybe "Emerald and
    Other Beryls" by Sinkankas or one of the Russians writing about the
    spectacular deposits of D'al Nagorsk. Can't remember, sorry. 

    I cut a LOT of larger synthetic corundum in "fancy" cuts, and some
    natural material as well. There is no question in my mind that the
    synthetic material is considerably more resistant to abrasion by the
    diamond sintered laps and hand-charged diamond/tin alloy laps I use
    than is the natural material, at least in the "soft" directions. In
    the "hard" direction, they are both just HARD! 

    I am surprised there has not been more work done on technical
    hardness (Rockwell or Knoop) and toughness of some of these
    crystalline materials according to their crystallographic axes.
    Maybe it's been done, but I sure can't find it. 

Wayne
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