Unlike sapphires and rubies, which share an extremely hard mineral called corundum as their source, garnets come from a group of stones, whose crystal structure is the same but whose chemical composition and colors differ. Minerals mined for garnets include the relatively common pyrope and almandine (what we think of as the traditional red carbuncle), rhodolite and spessartite (violet and orange, respectively), and tsavorite and demantoid (these green stones are the most valuable garnets in the world).
Red garnets are most common form of the gemstones, used in necklaces, bracelets, earrings, and rings. Pyrope contains iron, among other minerals, which gives its garnets a blood-red color. The stones were favorites of Victorian jewelers, while those in Bohemia (the present-day Czech Republic) have used garnets cut from pyrope for more than 500 years.
Almandine garnets are even darker, which is why they are sometimes carved out at the base to let more light filter through the gem. More brittle than pyrope, almandine garnets are susceptible to chipping, but this problem is offset by the stone’s ubiquity—they are found widely in metamorphic rocks around the world.
The chemical love child, if you will, of pyrope and almandine is rhodolite, whose garnets shade to a bright violet. In the U.S., these stones are mined in North Carolina’s Cowee Valley, which is also known for its rubies and sapphires. Internationally, rhodolite garnets are also found in Sri Lanka, Tanzania, and Kenya.
Spessartite garnets, which are orange, are relatively uncommon. Rarer still is the mandarin variety of the spessartite garnet, which is mined in Namibia. Similar in color, if not composition, are grossular garnets, which go by the name hessonite (a favorite gem of the ancient Greeks and Romans) and cinnamon stone. Malaya garnets from Madagascar vary in color from orange to cinnamon. Some malaya stones are considered so-called color-change garnets, which refers to a garnet whose hue intensifies when exposed to artificial light.
Finally there are the green garnets, which rival emeralds in appearance and wow-factor. Demantoids, which are mined in the Ural mountains of Russia, get their hue from chromium and are some of the most sought-after garnets in the world. Tsarvorite garnets are a relative newcomer on the gem scene, discovered only in 1967 near the Kenya-Tanzania border. In the 1970s, Tiffany’s named and marketed the gems around the world.