KAD-- Spectroscopy should separate garnet from spinel. You can get a
hand held spectroscope pretty inexpensively then all you have to do
is figure out how to wrestle the darn thing into submission so you
can read the spectrum of your sample. Very tricky to get the light
just right with a handheld, but with practice, practice, practice,
you can get a decent spectrum on many stones.
If you’re flush, the prism based units with stand, stone holder and
lighting are much easier to use. Once you develop skills and
confidence in using a good spectroscope, it’s one of the quickest and
most sure tests for many gem identifications.