Tsavorite

Grossular Garnet 
Color : Green, yellow, copper-brown
Mohs’ hardness : 7-7.5
Specific gravity : 3.6-3.65   
Chemical composition : Calcium aluminium silicate
Refractive index : 1.738-1.745
Double refraction: none

Discovered in the late 1960s in East Africa, this gemstone is a form of the common
mineral grossular garnet. The Scottish explorer and mining engineer, Campbell Bridges uncovered this fabulous gem while seeking tanzanite deposits which had also recently been found in the area. The name tsavorite was given this gemstone by Tiffany in honor of Kenya's Tsavo National Park. Similar crystals are also found in Pakistan. It is tougher and brighter than emerald which made it more suitable for setting. The rich green color in Tsavorite is caused by chromium and vanadium. 

There are two varieties of green grossular : one is found as transparent crystals, the other is massive. Massive green grossular from South Africa is called Transvaal jade, after its main locality and because it resembles jade. It may contain black specks of the mineral magnetite.