More than just a simulant for sapphire, tanzanite’s vivid hues have stunned the gem world. Since its discovery in 1967, this gem has become very fashionable. Indeed, for blue stones, only blue sapphire is more popular. This modern December birthstone originates in Tanzania, its namesake, where the only known deposits occur. Although this rare variety of zoisite does undergo heat treatment to reach its stunning hues, the color is stable and, unlike sapphire, doesn’t grey in artificial lighting.
Tanzanite Buying and the Four Cs
The IGS tanzanite value listing has price guidelines for top color tanzanite.
Zoisite with trace vanadium content heats at a relatively low temperature to produce gem-quality tanzanite, from purple to blue. Rarely, some stones found on the surface already show these colors. These occur due to natural heating by the Sun. Fortunately, heat treatment is stable and requires no further care.
Because of its original use as an inexpensive replacement for sapphire, the top desired color is a slightly violet blue. In these cases, the slight violet hue imparts a depth and warmth to the stone.
However, some connoisseurs prefer to treat tanzanite as tanzanite rather than an off-brand sapphire. The primary difference lies in…