Tanzanite is a spectacular blue, violetish-blue or bluish-purple variety of the mineral Zoisite, which is colored by vanadium. Initially discovered as small surface crystals in 1962, a large deposit was discovered in 1967 by a prospector in the Merelani Hills of northern Tanzania near the town of Arusha. This deposit turned out to be the only workable deposit of gem quality Zoisite known to exist. The American jeweler Tiffany and Company heard about the unusual material and quickly bought the rights as temporary sole distributor of the new gemstone. When first viewed by Henry B. Platt, great-grandson of Louis Comfort Tiffany, he proclaimed Tanzanite “the most beautiful blue stone discovered in 2000 years.” In 1968, Tiffany and Company launched an intense advertising blitz to inform consumers of this beautiful new gemstone that they named Tanzanite, after Tanzania, its country of origin. Drawn by the intensity of its color and velvety appearance in the best qualities, Tanzanite quickly caught on with consumers and continues to grow in popularity today.
Blue, violet and purple colors are known to occur naturally but are very scarce, so rough greenish-brown Zoisite is frequently heated to 752-932 degrees Fahrenheit (400-500 degrees Centigrade) to produce the memorable blue, bluish-purple to violetish-blue color for which Tanzanite is known. This treatment is permanent and considered acceptable by jewelers and consumers alike to the point where Tanzanite is presumed heated unless otherwise stated. Tanzanite should be cleaned only with warm slightly soapy water and should not be exposed to a steam cleaner or an ultrasonic machine.
When mining of Tanzanite first commenced it was not uncommon to find 20 carat to 50 carat fashioned stones of excellent clarity. Although fine clean larger stones are now scarce, beautiful material in the 10-20 carat range are still available. Although Tanzanite does not have a synthetic counterpart, there are simulants that closely resemble the natural material, including glass. A massive pink variety of Zoisite, called Thulite, is seen usually in more casual sterling silver jewelry. A massive green variety of Zoisite mixed with ruby is called Anyolite, and is predominantly used as carving material.
Varieties: Tanzanite, Cat’s Eye Tanzanite, Star Tanzanite, Thulite, Anyolite
Chemical Composition: Ca2Al3(SiO4)3(OH)
Colors: Blue, Violetish-Blue, Bluish-Violet, Bluish-Purple, Purplish-Violet, Pink, Green, Brown.
Crystal System: Orthorhombic
Refractive Index: 1.691-1.700 (+0.009)
Specific Gravity: 3.35
Hardness: 6 ½ - 7
Images by Paul Wild.