Francoise:
You were so helpful and authoritative re: the amethyst, I wonder
if you would tackle the issue of garnets. My price guides list
the species, but I see rough sold as “umba garnets” or "umbalite"
as well as the mandarin garnets which are supposed to be
spessartite and “mali garnets”. What are these?
Secondly, I have looked through my Liddicoat and several other
references and don’t see a procedure for differentiating the
garnet species or for dealing with mounted garnets. It appears
to me that sometimes RI is not enough as various species overlap
in the reported values. One can unmount and take a specific
gravity reading, but in some cases these overlap, too. I find a
few spectra listed. I have not puzzled all this out by making a
logic tree — I haven’t looked to see if, in the case where RI
overlap, the would clinch the ID or the spectra, etc. Can you
help? Or point to a reference. Thanks!