Imitations exist for every popular gem, and tanzanite is no exception. A few manufactured materials have a similar appearance to tanzanite. A synthetic forsterite (a mineral in the olivine solid solution series) is being produced with a color and pleochroism that resembles tanzanite.
Coranite is a synthetic blue corundum that resembles tanzanite. Tanavyte is a purple yttrium aluminum garnet that resembles tanzanite. Some blue glass has also been used as a tanzanite imitation.
Nanosital is a man-made glass-ceramic that is manufactured in a variety of gemstone look-alike colors. One of these is a bluish-violet material sold as a tanzanite simulant. It can easily be separated from natural tanzanite using a polariscope because tanzanite is doubly refractive while nanosital is singly refractive. Using a spectroscope, nanosital displays a spectacular spectrum, with numerous weak lines in the blue; a weak line and a strong broad band in the green; a very strong broad band near the yellow-orange boundary; and a broad weak band and a weak line in the red. Tanzanite might show bands at 455, 528 and 595. Another obvious test is pleochroism, tanzanite is spectacularly trichroic, while nanosital is not pleochroic.
Imitation materials cannot legally be sold as “tanzanite.” They must be labeled in a way that gives the buyer a clear understanding that the item being purchased is not natural tanzanite – it only “looks like tanzanite.”
Tanzanite imitations: A variety of man-made materials are used to simulate tanzanite. Shown here are a piece of Nanosital rough and a faceted stone. Nanosital is a Russian glass-ceramic that is made in a variety of gemstone look-alike colors. Nanosital is easily separated from the stones that it imitates with standard gemological tests.
Coated Tanzanite
Coatings of cobalt have been applied to some pale-colored tanzanites to improve their color. These treatments can be recognized by experienced jewelers and should be disclosed to the buyer. As always, buying from a reputable jeweler is the way to purchase with confidence.