is a Magnesium Aluminum Iron Boron Silicate Oxide Hydroxide Fluoride, and Vanadium also occured from Tanzania material. The formula is (Mg,Al,Fe)6Al4(Si,Al)4(B,Si,Al)(O,OH,F)22 and hardness of 6.5-7.
In fact the green material from Tanzania were sold as kornerupine but after testing from GIA,they found out that it was related to Kornerupine but known as Prismatine.
This gem here has been cut from material of the Stakholmen quarry,Hassela,Nordanstig,Halsingland,Sweden.
Size: 9.2x6.3x4.5 mm.
Weight: 1.94 ct.