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It might be possible to make coverslips with an RI close to that of water, at least the mineral cryolite has a
suitable RI and transmission characteristics - see below.

Jeremy Adler
NIMR
London



I came across a reference to a mineral called cryolite from Greenland in
Oliver Sack's book 'Uncle Tungsten'.  The interest is that the
refractive index of the mineral appeared to be close to that of water -
I work in microsopy a slide/coverslip of this refractive index would be of use.
Jeremy Adler
Nat Inst Med Res, Mill Hill

Thanks for your mineral enquiry, forwarded to me by our office.
The mineral cryolite is a naturally occurring fluoride of aluminium and
sodium, Na3AlF6. It is comparatively soft (2.5 on Mohs scale) with a
specific gravity of 2.97. It occurs most commonly in a massive form rather
than crystalline, although monoclinic prismatic crystals have been
described. It forms naturally in association with pegmatite veins close to
granite intrusions, although is now produced commercially as a synthetic
mineral for use in the manufacture of aluminium, white glass and sodium salts.
I'm not sure if this answers your question, but please let me know if you
need any further information.
Regards
Chris G. Jones

thanks for the quick response, it would be useful to know if there is a
measured refractive index for cryolite, rather than the relatively vague statement
in the book that it disappears in water.

Figures I can find state 1.33 at 500nm and 1.35 at 550nm, with a
transmission range of 250 - 14,000 nm.

Chris

At 15:39 30/10/03 +0000, you wrote: