GO 340 Gemstones & Gemology 
 Thulite. Photo date 4/02; © S.W. Aber. | Tanzanite is a member of the zoisite group, as is thulite, the national gemstone of Norway. Thulite is an opaque, pink gemstone usually cut en cabochon, and is named after Thule, an old name for Norway. The gem quality transparent zoisite, tanzanite, varies from a deep "sapphire" blue to an "amethyst" purple. It is a calcium aluminum silicate, Ca2Al3(O/OH/SiO4/Si2O7) (Schumann, 1997, p. 160). See The Image for another picture and general information. |  Image taken from Mineral Galleries |
 Image taken from Mineral Galleries | Tanzanite has a hardness of 6.5-7 and specific gravity of 3.35. It has both cleavage and an uneven fracture, and has an orthorhombic crystal system, which is reflected in the bladed crystal habit. There is no fluorescence, but it does have very strong pleochroism. Tanzanite is trichroic, purple, blue, and bronze colors. Tanzanite is doubly refractive, with refractive indices of 1.691 and 1.70. |  Tanzanite from The Image |
| Although zoisite was first found in Austria in 1805, tanzanite was not found until 1967. Tanzanite is named after the East African nation of Tanzania, found in a hilly area called Merelani, close to Mount Kilimanjaro, and the only locality this gem variety has ever been found (CW Jewelers, 1999 and Jewelery Central, 1999-2003). |  Tanzanite, heat treated. Image from Gem Hut. | It occurs as the vein or fissure filling mineral in metamorphic gneiss. The intense blue-violet color is caused by vanadium. Both crystal orientation and lighting conditions can reveal a dominant color and color is of prime consideration in the value of tanzanite. The blue or violet-blue are the most valued. |
 Tanzanite, heat treated. Image from Gem Hut. | Tanzanite does not have a history or lore because it was only recently discovered. Natural, rough tanzanite is usually a bronze color and has been known for some time. The new discovery was that heat removed the bronze color and brought out the blue-violet color. Masai herders, who drive cattle in the Merelani hills, came upon blue zoisite crystals after lightning had sparked a fire that swept through the area. This "blue zoisite" became "tanzanite" when it was introduced on the market in 1969, by Tiffany & Company (CW Jewelers, 1999). Contrary to rumors, tanzanite mining has no connection to funding terrorism. For more information visit an Arizona Daily Star story, U.S. clears tanzanite of terroist connection. |
 Image taken from Mineral Galleries |
| Various lighting conditions have noticable effects on the color of tanzanite. According to (CW Jewelers, 1999), morning sunlight adds red, orange, or yellow, making the gem look more purple; overcast natural light adds blue and gray; incandescent light adds red which strengthens purple colors and turn blue to a violet color; fluorescent light strengthens the blue; halogen lighting adds sparkle and strengthens the purple. |
 Image taken from www.asherjewelry.com/ Asher Jewelry | Tanzanite is a highly valued gemstone and is priced just below emerald, ruby, and sapphire. Tanzanite can be synthesized and it is imitated by treated beryl, glass, and assembled stones. Doublets and triplets are made with a tanzanite crown and colorless synthetic spinel pavilion or two colorless synthetic spinels with a tanzanite colored cement holding the crown and pavilion together. |
To learn more about tanzanite visit:
Introductory image taken from Jewelry Central.
References
Return to the Syllabus or choose another gemstone below.
| Alexandrite | Amber | Amethyst | Chalcedony | Diamond | Emerald |
| Garnet | Jade | Malachite | Opal | Pearl | Peridot |
| Ruby | Sapphire | Tanzanite | Topaz | Tourmaline | Turquoise |
This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: saber@emporia.edu Thanks for visiting! Webpage created: November 15, 2000; last update: June 30, 2007.
Copyright 1999-2007 Susan Ward Aber. All rights reserved.