The green variety of grossular garnet, discovered a few decades ago and found mainly in Kenya, near the Tsavo National Park, is also known as Tsavorite (or Tsavoiite).
Appearance It is a light, verdant, or dark green, similar to the color of the better green tourmalines and sometimes, it is said, even comparable to African emerald. It has good luster. These gems, which are usually given a round or pear-shaped mixed cut, or occasionally a brilliant cut, are generally small, rarely exceeding one carat and never more than a few carats.
Distinctive features Being singly refractive, green grossular is distinguished from green tourmaline, by the latter's strong birefringence and pleochroism, and from many green zircons, which are obviously birefringent, whereas measurement of the physical properties is necessary to distinguish it from green sapphire when the latter does not display clear pleochroism. lt is very similar in all respects to a recent artificial product of comparable structure, namely green YAG (Yttrium Aluminium Garnet), from which it is distinguished by its physical properties.
Occurrence It is very rare; being found mainly in Kenya and Tanzania, but also in Pakistan.
Value If a good color (a lively, strong green), it can be in the top price bracket for secondary gems; this is especially true of the very rare examples weighing a few carats. Little known by the general public, it is in demand by collectors and connoisseurs.
Simulants and synthetics Green grossular has only been known for a few decades. Green YAG (an artificial product with the structure of garnet, but not containing sillcon) closely resembles it and can be a good imitation. it is not produced synthetically.