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Roger Weller, geology instructor                     

Linda Coe
Physical Geology
Fall 2005


photograph by Roger Weller

Where found?: Only in a 13 sq. kilometer area in the Merelani Hills, near Arusha, Tanzania, South Africa (west of Rwanda).

When discovered?: 1967

What is it?: Ca2Al3Si3O12(OH)
Mineral:  Zoisite

Who discovered it?: Pastoral Massai herdsman first discovered tanzanite near Mt. Kilimanjaro.

Hardness:  6.5 to 7.0 on Moh’s scale   

Color:  Purple, blue-violet, blue

photograph by Roger Weller

Trichroic: Pleochroic: Shows different colors in 3 different directions when viewed by transmitting light.

Crystal system: Orthorhombic with 3 unequal axes intersecting at right angles.

Mineral Associations: Hornblende, Almandine, Glaucophane

Cleavage: Perfect in one direction.
Price: $100 for 1 gram in 2001    (One gram equals 5 carats)

           $700 for 1 gram in 2004


Home cleaning:  Use lukewarm water with a mild soapy solution. Clean with a small brush, esp. on the back where dirt collects. DO NOT USE ultrasonic machine. Be careful tanzanite can break or chip!


Tanzanite falls into a  gem class right behind the ruby, emerald, and sapphire. This highly sought after exotic stone is mined in only one place in the world. Tanzania.

            When this 20th century stone is first mined, it is a brownish-yellow color. Heat is added (600 degree Celsius) to enhance the brilliant colors of purple and blue.

photograph by Roger Weller


The best tanzanite stone to buy is the darker one in opposition to the lighter colored one.  It is better to buy this one in a necklace or broach compare to a ring, because even though it is a hard stone, it still can chip!

photograph by Roger Weller


            Recently, a large stone was found weighing 3 kilograms or 16,839 carats. They have named it “The Mawenzi”.  Now there will be more Tanzanite for us to enjoy.

            Better get out and BUY some before its mines are depleted.

photograph by Roger Weller


Forecast Future: Value will continue to go UP!


Works Cited


Modern Jeweler. Melville: Sep 2005. Vol. 104, Iss. 9;  pg. 19, 1 pgs