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Posted in response to Ok Faceters from Ward on December 06, 2007 at 19:26:50:

Re: Ok Faceters

Hi Ward,

While quartz is a member of the isodametric class of anisotropic crystals, it is weakly birefringent (nε - nω = .009) and does not possess any distinct cleavages of consequence to faceters.

You really don't need to concern yourself with crystallographic axes when orienting your amethyst for faceting. Of more relevant concern with quartz is orientation for best yield and the shape you want to cut, orienting out inclusions or other defects in the rough, and orienting color zoning in the crystal.

If your crystal exhibits color zoning, placing the zone of best/most saturated color in the culet area of the pavilion will produce the richest color stone. If you have a dichroscope you may already be well acquainted with the jargon of optical crystallography. If not, here is a primer for you:
http://rockhounds.com/rockshop/gem_designs/refractive_index/index.shtml

If you want a lot more depth and detail, here is a good book on the subject:
http://rockhounds.com/rockshop/books/faceting.shtml#optical_crystallography

Good luck with your amethyst, and may all your scratches be little ones. :)

From Bob Keller - December 06, 2007 at 20:21:09

Message: 65639

Message Index Start New Topic Photo Gallery FAQ and Use Tips Bob's Rock Shop

Bob Keller