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Learn About Tanzanite Gemstones



Tanzanite Gemstone Properties
Tanzanite, the birthstone for December, was discovered in 1967. It really took the gemstone world by storm in the late 1980’s and 1990’s. A tremendous amount of high quality Tanzanite gemstone production caused prices to plummet. As a major buyer of Tanzanite rough gems, I was very apprehensive when I was presented with 5 kilogram lots of Tanzanite! As a consequence this beautiful blue gemstone with lavender tones became affordable to the mass jewelry market and jewelry consumers. In spite of its appealing trade name, Tanzanite is just the blue lavender form of the mineral Zoisite. Zoisite occurs in many other colors, green, yellow, and pink. Tanzanite has a hardness of 6.5 on the Moh's scale. It is suitable for jewelry, if care is taken in the style of mounting chosen so that the gem is not overly exposed in the mounting. It should never be put into an ultrasonic cleaner or worn everyday as other harder, more durable gemstones. Tanzanite is only mined in one area of the earth, the Merelani hills near the northern Tanzanian towns of Moshi and Arusha. The tanzanite gems are found in sausage shaped pockets of schist, sometimes at great depths. Most Tanzanite gems are found in irregular crystal shapes and are a dark brownish color. Once heat treated to 600 Celsius, a stunning transformation takes place to the famous blue-lavender color. The heat treatment is permanent and the color cannot be enhanced further with more heat treatment. The mesmerizing blue color with secondary lavender tones and pinkish red flashes is a result of Tanzanite’s trichroic crystal structure, that is, it shows different colors when viewed in different directions. One direction is blue, another purple, and another reddish pink, if the quality is good enough.

Tanzanite Gemstone History and Lore
Tanzanite was discovered by some Masai herdsman who were tending cattle in the Merelani Hills. Legend has it that the affect of heat was first discovered when some brown Zoisite crystals laying on the ground with other rocks were caught in a fire set by lightning that swept through the grass covered Merelani hills northeast of Arusha. Masai herders, who drive cattle in the area, noticed the beautiful blue color and picked the crystals up, becoming the first Tanzanite collectors. These crystals brought a Portuguese geologist to the area by the name of DeSouza who recognized this extraordinary find of an exciting new gemstone. It was Tiffany's, the famous jewelry store, christened this newly discovered gemstone Tanzanite - in honor of the country of its origin and only known source. Tiffany’s recognized this gemstones potential and promoted the gemstone to the public. Tanzanite is now one of the five top selling colored gemstones in the USA and world. Tanzanite was recognized as a birthstone for the month of December just recently.

Tanzanite Gemstone Sources and Occurrences
There is only one commercial source for gem quality Tanzanite. It is the Merelani hills near the northern Tanzanian towns of Arusha and Moshi. The mining area extends along a gem bearing belt of approximately 4 miles. There have been a few undocumented Tanzanite gems discovered in Kenya, but nothing of any significance. The Tanzanite deposit is very large, but the primitive mining techniques coupled with unprecedented demand, has significantly curtailed production - especially of the better quality Tanzanite gemstones.

Tanzanite Gemstone Evaluation and Valuation
Color intensity is the most important consideration when choosing a Tanzanite. Size is not a consideration in Tanzanite valuation, as Tanzanite is commonly found in very large, flawless crystals. Tanzanite should be free of inclusions. I have seen a 200 gram, completely clean gem crystal! Depending on the orientation of the cut, the color can be either blue or lavender, if it is perfectly oriented along that color axis. This is rarely the case and almost all Tanzanite gems are a dominate blue color with a touch of lavender. Neither is considered more valuable or rare, but the purer blue color gets the higher prices, especially in the Asian markets. As with any gemstone the cut is also of prime importance, as the better quality of cut will bring out the gemstone's luster and brilliance.