Tanzanite
Tanzanite Information
WEARABILITY* Good
ENHANCEMENTS Virtually all tanzanite is heat treated
*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
CHEMISTRY Ca2Al3(SiO4)3(OH)
CRYSTALLOGRAPHY Orthorhombic
REFRACTIVE INDEX 1.692 - 1.700
HARDNESS 6 - 7
SPECIFIC GRAVITY 3.35
CLEAVAGE Perfect
HEAT SENSITIVE Yes
SPECIAL CARE INSTRUCTIONS Avoid rough treatment
For more details see the article on "Hardness and Wearability."
...Few gems have attained the popularity of Tanzanite in such a short period of time. The gem was only discovered in the 1960's and soon the demand raised the prices to a very respectable level. The government of Tanzania promoted this gem with an expertise that would make DeBeers proud.
... In 1995, while the Internet was still young, I received an email from a college student in Canada. He was commissioned by the Tanzanian government to assess what could be done to raise the demand in Canada. I was surprised, because the demand already exceeded the supply.
... Tanzanite is a beautiful gem, but with moderate hardness and perfect cleavage, it is less than ideal for wearing in jewelry. Its closest look-alike, iolite, wears much better and costs less. Therefore, much credit has to be given to a world-class promotion of this gemstone.
... The source for tanzanite is one small area in Tanzania. All the upper layers have been worked and the latest sources are from substantial depths. The mines closed right after the 1998 Tucson show. Heavy rain, flooding, and cave ins caused several dozen deaths.
... Click here to see a vast collection of fine Certified and Natural Tanzanite gems.
... To reopen the mines requires considerable reinforcement. None of the local miners will go back into the holes, so a foreign crew would have to be brought in. Several large corporations have looked into taking over the mines, but none have attempted it because the cost is too great.
... Even though the supply diminished considerably, the demand for tanzanite remains high. New sources have been discovered that are somewhat removed from original source. However, the deposits are small and the production is not nearly enough to equal demand. Prices have skyrocketed and are expected to remain high for several years. They will not go down until the demand for this gem finally settles.
... Since the mines closed, prices have varied wildly. Before closing, top quality tanzanite, in the one to three carat range, wholesaled for $100 a carat and would retail between $175 and $300. Today, gems in the same size range, with moderate color saturation and eye visible inclusions, typically sell around $400 a carat. Fine quality gems can demand over $1000 per carat.
... Tanzanite is a variety of zoisite, which is a member of the epidote group. The particular coloring that distinguishes tanzanite is only found in Tanzania. As it comes from the ground, it is primarily brown, although many stones show some purple. By heating the stones to approximately 700 degrees Celsius, a pleasurable color change takes place.
... The quality of rough can be evaluated by its tone, (its relative lightness or darkness.) The tone doesn't change during heating; it just goes from brown to purple and blue. So the darker the tone before heating, the higher quality your finished goods will be.
... After heating most tanzanites are just purple, with approximately 1/3 of the pieces showing blue in one direction. About half of these will be oriented so you can get maximum yield cutting for the blue color, or about 1/6th of each lot. Every once in a while you will also find a very rare green tanzanite.
... Blue tanzanites are more desirable than the purple. Before the primary mines closed, they brought a higher price. Now the distinction between blue and purple gems no longer has a substantial affect on the price.
... Click here to see a vast collection of fine Certified and Natural Tanzanite gems.