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What is rainbow Garnet?

hi All I just a few samplings of this material at a studio,and was
wondering if anyone can shed some light on the material,it is
beautiful material in my mind but it is pretty nasty from a fine gem
quality garnet’s point of view. actually it was also very pricey.$25
to $75 a stone ,cabochons 15mmx5 30mmx8mm any hints any one?


It’s probably another name for a material also being marketed as
"Watermelon Garnet." It’s a mixture of hydrogrossular garnet
(red/pink) and idocrase (green) that you find listed in most gem
references as “Transvaal Jade.” The massive material, cut only as
cabochons, has been mistaken for and even marketed as jade because of
its mottled, translucent appearance.

According to an article I read some time back it was discovered in
South Africa in the 1940s and was stockpiled by a dealer in
Idar-Oberstein, Germany. A Connecticut gem dealer came across the
German stash recently and bought the whole lot, about 4 tons. Only
about 50 kilos were salvageable as gem material. Samples of cut
stones I’ve seen are quite attractive with lovely pastel colors
swirled together in interesting patterns. I find the pink colors
very attractive, almost exactly the color of watermelon. The prices
you were quoted seem about right, although larger pure pink pieces
are being sold for lots more.

Rick Martin

Dear Rick, Inspite of having spent a great deal of time in Africa I
never had any exposure to Traansval Jade. On the other hand, I have
always had a keen interest in our own Traansval Jade…the
idocrase/white grossular jade simulant that has been mined in
various California localities, especially in several North Coastal
Range sites. I have had considerable success with cutting and cabbing
this material and it has at least as much appeal as most jades while
retaining most of the desirable physical charateristics usually
associated with jade. Another variant of this material is the
vesuvianite occurence in Plumas County, CA. This idocrase is highly
translucent and strongly resembles peridot. Later, Ron at
Mills Gem, Los Osos, CA.

“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. your briolette specialist