Tanzanite Gem Properties

One of the most exciting gem discoveries of the twentieth century is tanzanite, which was first seen in Tanzania in 1967. It was publicized by Tiffany & Co. It has a vibrant blue to blue violet color and can easily be mistaken for the finest sapphire.

Tanzanite, Tanzania
Photo by ICA/Bart Curren

If you are looking at a tanzanite it is critical to view it under different lighting conditions. In daylight tanzanite will display the most blue, incandescent light will bring out the violet color. Generally those stones that are brilliant blue with minimal violet, even in incandescent light, will command the highest price. If you prefer the violetish shades you will pay less.

Colors: Blue to violet
R.I.: 1.69 – 1.70
Durability: Fragile
S.G.: 3.20 – 3.40
Treatment: Assume heating
Hardness: 6 – 7
Availability: Supply meets demand
Localities: Tanzania
Price: Moderate to expensive
Common shapes: Oval, cushion and fancy shapes available

Before the incredible blue shade is created by heat, resulting in tanzanite, the zoisite is a greenish to brownish color which is extremely trichroic. There is some zoisite that has been naturally heated by the sun to turn the material to tanzanite, but most is gently heated before cutting.

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Green chrome zoisite. Photo by ICA/Bart Curren
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By Sondra Francis - Copyright © Sondra Francis, G.G. 1999
About the Author: Sondra Francis has scoured every major colored gemstone market in the world since 1978. She was a charter member of the American Gemstone Association and served as a board member. She was a founding member of the International Colored Gemstone Association. A true gem lover, Sondra has marketed her treasures on the wholesale and retail markets.
Acknowledgments: A special thanks to Pam Dulgar, Alex Edwards, Cheryl Kremkow, Kate Kirby, Helen Mitchell, Carol Morgan Page, David Pond, Elaine Proffitt, and Ray Zajicek for their help.
Photographs: Bart Curren and ICA Gembureau ; Alex Edwards, Pearl Sales Institute ; David Dikinis
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