Green Garnet

Tsavorite forms in metamorphic rocks but is rarer than red garnet because it needs unusual rock chemistries; Mindat gives Kenya and Tanzania as its major occurrences. Demantoid was first discovered in Russia's Ural Mountains in 1851 and has also been found in Italy, Iran and, more recently, Namibia (1996). IGS lists mint grossular from Merelani, Tanzania, and massive green grossular from Pakistan and South Africa.

Demantoid is recognized by its strong fire and its characteristic radiating "horsetail" inclusions of byssolite; GIA notes these inclusions are among the few that increase a gem's value. Grossular often shows a swirled, granular "treacle" look under magnification and may show anomalous double refraction. Lab-made yttrium aluminum garnet (YAG) has been offered as tsavorite. IGS also reports that gamma irradiation can give colorless or pale grossular an unstable yellow-green color that fades in sunlight within hours to days, so examining yellow-green grossular in sunlight is advisable. Massive green hydrogrossular from South Africa sold as "Transvaal jade" is garnet, not jade.

GIA notes that garnets are stable to light and chemicals but can be attacked by hydrofluoric acid; they have fair to good toughness and should be protected from hard blows. Warm, soapy water is always safe, an ultrasonic cleaner is usually safe except for fractured stones, and steam cleaning is not recommended. Garnets might rarely be fracture-filled; such stones should be cleaned only with warm, soapy water. Hardness ranges from 6.5 to 7.5 depending on type; tsavorite is on the harder side, while demantoid is a bit softer.

Demantoid, whose name means "diamond-like", was popular in Russia from its discovery in 1851 through the early 1900s and appears in jewelry by Carl Fabergé; Tiffany & Co. also used it extensively when George F. Kunz was its chief gemologist. Tsavorite was first discovered by the gemologist Campbell R. Bridges in north-east Tanzania; it was mined in Kenya near Tsavo National Park, and the name was proposed by Tiffany & Co. president Sir Henry Platt after Tsavo East National Park.

Garnet is the birthstone for January and the gem of the second wedding anniversary.