Tanzanite Technical Information

Tanzanite Fact Sheet:

• Name:
  

• Tanzanite (zoisite)
  

• Chemical:
  

• Ca 2 Al 3 Si 3 O 12 (OH)
  Hydrous calcium aluminum silicate
  

Zoisite : A grayish or whitish mineral occurring in orthorhombic , prismatic crystals , also in columnar masses . It is a silicate of alumina and lime , and is allied to epidote . Origin: After its discoverer, Von Zois, an Austrian mineralogist.

Source: Websters Dictionary

• Crystal:
  

• Orthorhombic (long striated crystals, also bladed crystals)
  

• Color:
  

• Gray, yellow brown, pink (thulite), blue-purple (tanzanite), greenish
  

• Refrac. Index:
  

• 1.69-1.70
  

• Birefraction:
  

• 0.009
  

• Hardness:
  

• 6.5-7.0
  

• Spec. Gravity:
  

• 3.35
  

• Fracture:
  

• Uneven
  

• Cleavage:
  

• Perfect
  

• Environment:
  

• Restricted to metamorphic (volcanic) rocks
  

• Association:
  

• Hornblende, Almandine, Glaucophane, Graphite
  

• Locales:
  

• Norway (thulite) | Tanzania, East Africa | N.C., Calif., USA |
  

• Misc:
  

• Named for its locality, Tanzanite (from Tanzania) where the only transparent gem variety is found. Thulite is named after Thule, an archaic name for Norway. Tanzanite possesses strong pleochroism from blue-violet to violet.
  

• Gem info:

• The gem variety, tanzanite, is a very rare gemstone as there is only one place it has ever been found. Tanzanite was found in this locality in 1967, and it is today about exhausted. The stone is said to have low tolerance to ultrasonics, and should not be subjected to this method of cleaning.

• Tanzanite is a fairly high valued gemstone and falls in a class just below the three big colored stones, emerald, ruby and sapphire (which it resembles). Tanzanite rough is most often heat-treated to enhance its color and remove any yellow or brown overtones.
  Thulite is a cabbing material and is not found in transparent rough. It is usually pink to brown in color.