“Rainbow garnet” was brought to market about 10 or 12 years ago.
Although previously known, it never made it into main-stream before
and remains relatively unkown still. Mostly due to very low supply
of quality goods. This could change though.
It is an andradite garnet from Mexico…Sonora I believe. Generally
it is opaque to transluscent grayish green-olive. The better stones
will show a rainbow of colors due to interference phenomenon (like
oil on water). They often exhibit a patchy mosaic pattern of
"rainbow" colors and are truly unique and different than anything
else in the gem world.
Cutting this gem requires a skilled eye to remove material that
hides the “rainbow” layer similar to a fire agate in cutting
principals. If the cutter goes too far the “rainbow” layer can be cut
through or removed entirely.
This garnet may sometimes have 4 ray stars too. Not many top quality
stones were ever found. The best ones brought thousands of dollars
and were never much over 5cts or so. There were very few of this
quality. They were truly unique and beautiful. Most have faint to
medium “rainbow” intensity and are not very marketable.
If there were ever a larger supply of high quality “rainbow” garnets
this would be a major gemstone and big business.
The same deposit also produced some clear transparent stones that
qualify to be called Demantoid, although not the best color.
Hope this helps, Steve Green
Rough and Ready Gems, Inc.
www.briolettes.com your briolette specialist