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What is Rainbow Garnet?

Hi All,

After I’d posted speculating that “Rainbow Garnet” was another name
for “Watermelon Garnet a.k.a. Transvaal Jade a.k.a.
hydrogrossular/idocrase,” I remembered what it probably really is.
But my computer was down and I couldn’t post.

The African hydrogrossular is always cabbed and is currently “new”
(again) on the market, and that’s what made me think of it. Then I
remembered another type of garnet, other than star garnet, that’s
always cabbed: an unusual type of grossular/andradite from Mexico and
one location in Nevada. The best of these stones throw off a bright
play of colors in reflected light that could give rise to the
trade-name “Rainbow Garnet.”

I believe the material currently being sold is coming from an
andradite location in Mexico. The only data I have is on the Nevada
material. It is honey-colored to dark brown and the reference I have
says the play of color is caused by lamellar twinning, a structure
somewhat similar to the twinning in microcline feldspar that causes
the “rainbow” in Labradorite.

Rick Martin

Lapidary Journal did an article on the Mexican rainbow garnet in the
early '90s. I can’t remember precisely when, but it must have been
sometime in 1993 or 1994, because it was while I was still working at
the magazine. If you drop a note to LJ, perhaps someone there will be
able to give you the exact publication date.

Suzanne Wade
Phone: (508) 339-7366
Fax: (928) 563-8255