Tsavorite

Tsavorite is the vivid green, vanadium- and chromium-colored gem variety of grossular, a calcium aluminum silicate species of the garnet group. Tsavorite forms during regional metamorphism of graphite-bearing, calcium-rich sedimentary rocks at moderate to high pressures and temperatures (500-700°C). The critical ingredient is vanadium (and sometimes chromium), which substitutes for aluminum in the grossular garnet structure to produce the vivid green color.

The crystals grow within metamorphic rocks where graphite acts as a reducing agent, keeping the vanadium in the correct oxidation state for green coloration. Most tsavorite crystals are found in relatively small sizes because the geological conditions that produce them also tend to fracture and break larger crystals during ongoing tectonic activity. Stones over 2 carats are uncommon, and anything over 5 carats is exceptionally rare.

Discovered in 1967 by Scottish gemologist Campbell Bridges in Tanzania, it was later found across the border in Kenya near Tsavo National Park. Tiffany's Henry Platt named it 'tsavorite' and championed its introduction to the gem market in 1974.

Tsavorite's vivid green color, high refractive index (1.740), and lack of inclusions visible to the naked eye distinguish it from emerald, which almost always has visible inclusions. Under magnification, tsavorite may show graphite crystals and actinolite needles as characteristic inclusions.

Distinguish from chrome diopside (softer, lower refractive index), emerald (lower RI, typically included), peridot (different green tone, double refraction), and chrome tourmaline (different crystal system). Tsavorite is singly refractive as a garnet, which separates it from most green gems.