Garnets: A Rainbow Of Color

How many of you with January birthdays know that your birthstone, garnet, comes in colors other than red? Garnets can be green, yellow, orange, black, violet, and of course, red.  According to the GIA (Gemological Institute of America), garnets are divided into more than 20 categories. They are collectively known as the garnet group.

The garnet group is a set of minerals which are closely related in terms of crystal structure and chemical composition. Within the group, the gems are divided into species, and some of those species are further subdivided into varieties.

Garnet Group chart

Some Garnet Trivia

  • The name “garnet” is thought to be inspired by the vivid red crystals which can look like pomegranate seeds. The name comes from the Latin word for grain or seed: granatus.
  • A 5,000 year old garnet bead necklace was found in a grave in Egypt.
  • The Bohemian mine (in modern-day Czechoslovakia) began mining red garnets in the 1500s, resulting in a regional jewelry industry that peaked during the late 1800s.
  • Campbell Bridges discovered Tsavorite Garnet in 1967. Tsavorite is a bright green, easily mistaken for emerald, and is part of the Grossularite garnet species. Although he first discovered it in Tanzania (where he also discovered Tanzanite), Bridges traced the line of the deposit back to Kenya, and wanted the gem named after Tsavo National Park.

Demantoid Garnets: The “Emerald of the Urals”

The rarest and most valuable garnets are the brilliant green demantoid garnets (a variety in the Andradite garnet species). The name means “diamond like lustre” and they do indeed exhibit fiery flashes of color, as diamonds do. Demantoids were discovered in the Ural mountains in Russian in 1853, and that remained the only known source until 1996, when a major find was discovered in Namibia (the Green Dragon mine). Russian demantoid garnets can exhibit what is called “horsetail” inclusions, and this phenomenon makes them even more valuable.

horsetail inclusions in a Russion demantoid garnet

More recently, deposits have also been found in Madagascar, Afghanistan, Italy, Iran, China, Korea, Zaire, and the United States. Demantoid garnets are usually small (stones larger than 1 carat, or about 6mm in diameter, are rare), so if you see a large stone advertised as a demantoid garnet, be suspicious.

Color Change Garnets

A few garnets exhibit a very rare phenomenon known as color change — their color changes based on the light source (e.g. under a lightbulb versus under sunlight).

One such variation is:

  • In incandescent light (light bulb): color is pink to red
  • In sunlight or fluorescent light: color changes to greenish-yellow
180115_color change garnet_2
color change garnets

A second variation might be:

  • In incandescent light (light bulb): color is grayish violet to purple
  • In sunlight or fluorescent light: color changes to greenish-blue or violet

More Than Red

Garnets come in such gorgeous colors that it’s hard to pick a favorite, but I have to admit I’m partial to the fiery brilliance of the demantoids and the rich purple-red of the rhodolites. Remember, garnets are more than red!

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