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In article <hiLJf.806978$xm3.134801@attbi_s21>, George wrote:
> Perhaps they were confused by the double refraction of the calcite lens.
>
Nope. IIRC (but I may have to get Fortey's Blue Book off the shelf.
Or Clarkson's tan book, for that matter.) the optical axis of the calcite
crystals is parallel to the triclinic axis of the calcite. Uniaxial
mineral, and isotropic in that direction. Hmmm, I had to do too much
spinning crystals in my mind's eye for that. Better check.
Wikipedia isn't very informative.
--
Aidan Karley FGS
Aberdeen, Scotland,
Location: 57°10'11" N, 02°08'43" W (sub-tropical Aberdeen), 0.021233
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