January’s Birthstone Fun Facts: The Cool Factor of Garnet Gemstones

No tale of garnet gemstones would be complete without a variety of fun facts. After all, it’s things like this that make birthstones special.

ABOVE: Spessartite garnets, like this 7.98 carat oval, have been known as mandarin garnets, probably because their color is similar to a mandarin orange. Photo Mia Dixon, courtesy Pala International.

Garnets are hard and tough gemstones, and as a result, they’ve been used as abrasives in industry forever. Garnet powder was possibly used by the Chinese in the carving of jade centuries ago. Garnet is also the “emery” in emery boards and emery sand paper.

gemstones: color-change garnet

Change color gemstones are fascinating: one color in incandescent light, another color in fluorescent or daylight. This 1.79 carat pear-shaped color-change garnet, cut by John Bradshaw, shows a distinct change. It’s green in daylight and pink in incandescent light. Photo courtesy John Bradshaw and Coast-to-Coast Rarestones International.

One of my favorite uses of garnet is in the creation of glass/garnet doublets. In the past, very thin slices of red garnet were fused to glass of any color. Once fused, “gemstones” were cut from the lump in such a way that the garnet slice was located on the crown of the stone, usually forming the table and at least parts of the crown facets around the table.

Why was this done? Because of garnet’s hardness. The garnet table/star facets made the glass imitation wear longer.

Glass garnet doublets have been used to imitate all other gemstones. Weirdly, unless you turn the stone over, you won’t see the red of the garnet–not even in colorless doublets! When you flip the stone table down, though, from the pavilion you can see a red ring circling the crown. I don’t know if these doublets are made anymore, but it was always my favorite identification problem for gemstones in school. Very easy to spot if you remembered to look for the ring.

gemstones: pearl-shaped grandite garnet

This lovely pear-shaped yellow grandite garnet, also known as a Mali garnet for its source in Africa, weighs 5.37 carats. Photo Mia Dixon, courtesy Pala International.

Garnet is an indicator mineral for diamonds. Geologists searching regions where they suspect diamond deposits are located may look for tiny garnets lying on the ground. These tiny fragments are brought to the earth’s surface by industrious ants as they clear their tunnels of the obstacles. The presence of the tiny gemstones means there could be a diamond pipe under that ant hill.

Garnets are so closely associated with diamonds that blood red inclusions of garnet crystals have been found in diamonds. If you have access to the Photoatlas of Inclusions in Gemstones, by Edward Gubelin and John Koivula, you’ll find a number of superb shots of these inclusions.

Even if I didn’t love garnets for their color, I’d love them for their “cool.”


Sharon Elaine Thompson is a GG and FGA who has been writing about gemstones and jewelry for Lapidary Journal Jewelry Artist since 1987. She also writes a line of birthstone romance novels under the name Liz Hartley.


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