Jean Louis, Manager of Tanzanite polishing and trading office
Tanzanite has certain unique quality that it is to show you different colors depending from which side you are looking at it.
Almost all Tanzanites are heated to gain more of the blue color. Even a heated Tanzanite will show you from one side blue and other side violet color. Observe it properly.
There are other ways to determine if Tanzanite is real such as Hanneman Tanzanite filter or physical measurement of the specific gravity, spectrometer and hardness tests which I do not recommend on polished gemstones.