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Tanzanite is one of the traditional birthstones for the month of December. 

Tanzanite is the dark blue variety of Zoisite and is sometimes mistaken for a sapphire. It is frequently heat-treated to remove any brown patches and enhance its color. A red tint seen looking down the c-axis is a good indication that the crystal coloration is natural. Note also that tanzanion is used as a synthetic stimulant for tanzanite. Tanzanite crystals have distinct pleochroism and show gray, purple, or blue depending on the angle from which they are viewed. The faceter must orient the stone carefully for the best color. Cut tanzanites may appear more violet in incandescent light. Tanzanite comes from Tanzania and Pakistan. 


Zoisite crystals are prismatic and vertically striated and can be yellow-green, green, white, green-brown, or gray. The most valuable is tanzanite, colored sapphire-blue by vanadium. A massive, pinkish-red variety is called thulite. Zoisite is a calcium aluminum silicate hydroxide (Formula: {Ca2}{Al3}(Si2O7)(SiO4)O(OH) ) and belongs to the epidote group. It is characteristic of the hydrothermal alteration of igneous rocks. It is also found in quartz veins and pegmatites. Localities include Spain, Germany, Scotland, and Japan. 

As the most common story of the tanzanite mining boom goes, in 1967 a Masai tribesman stumbled upon a cluster of highly transparent, intense violet-to-blue crystals weathering out of the earth in Merelani, an area of northern Tanzania. He alerted a local fortune hunter named Manuel d'Souza, who quickly registered four mining claims. D’Souza hoped that he’d been shown a new sapphire deposit. Instead, the deposit contained one of the newest of the world’s gems.

Although it’s a newcomer to the gemstone industry, tanzanite has quickly become one of the most popular colored gemstones. - Courtesy Richard Krementz Gemstones
Within a short time, 90 more claims appeared in the same 20-square-mile area. No one was quite sure what the beautiful crystals were, but everyone wanted to lay claim to the profits they were certain to produce. The new gem would eventually be known as tanzanite, and it would, at times, rival the Big 3 in popularity. Due to the influx of miners, de Souza was unable to maintain control over his mining claim. In 1971, the Tanzanian government took over the mines and in 1976 they handed it over to the State Mining Corporation. 

Tiffany & Company recognized its potential as an international seller and made a deal to become its main distributor. Tiffany named the gem after the country it came from and promoted it with a big publicity campaign in 1968. Almost overnight, tanzanite was popular with leading jewelry designers and other gem professionals, as well as with customers who had an eye for beautiful and unusual gems.