Cochise College Student Papers in Geology
Geology Home Page physical geology historical geology
Roger Weller, geology instructor regional geology planetary gems
wellerr@cochise.edu
Tanzanite
by Mary Lugo
Physical Geology
Spring 2008
Journey
with Tanzanite
Considered to be the gemstone of our generation, Tanzanite is taking the world
by storm. A thousand times rarer than a diamond, tanzanite is mined in only one
place in the world where new diamond deposits are discovered nearly every month.
Found in the Merelani foothills of Mount Kilimanjaro, Tanzanite was discovered
by the rest of the world in 1967. Tanzanians had long discovered this beautiful
stone but decided to keep its beauty to themselves. This gemstone was discovered
by a tailor named Manuel d’Souza. While searching for Rubies d’Souza was led to
the deposit of blue stones, by tribesman. Campbell R. Bridge (Tiffany & CO.
employee) was the first person to bring Tanzanite to the United States.
Tanzanite was the given name that Tiffany & CO. gave to the blue Zoisite.
photo by: http://www.tanzaniaodyssey.com/maps-of-tanzania-game-reserves--islands/map-of-tanzania.htm
Legend has it
a lightening bolt struck the ground causing a grass fire. The heat from the
grass fire caused the Zoisite to change to a violet, blue color, and was
discovered by a herdsman. Heat created by a grassfire is not strong enough to
change the color of Zoisite, but heating treatments are used in the color change
process. First Generation miners placed the gemstones into charcoal fires to
change the color. Today heat treatments are used to lighten, darken or alter
color of gemstones. Tanzanite can be heated to a temperature ranging from
500ºC - 620°C (932°F).
Tanzanite is usually a yellow,
brownish color when mined. A thermal shock is needed to change the color of the
gemstone. This gem, once changed, encompasses the majestic purple mountains
being covered with the evening blue skies. Tanzanite is a color changing
gemstone. Incandescent (candle light) lighting causes the purples, lavenders,
lilacs, and periwinkles to shine, but when placed in the sunlight the many
shades of blues will shine. “Tanzanite is a gemstone that would not be
available in commercial quantities if it wasn’t heat treated” (Guides to Gems
and Jewelry). Thermal heating of gemstones is widely accepted as natural or
genuine and not lab created or simulated.
Photos © - Tanzanite One Ltd
http://www.tanzaniteone.com
Photo by
www.gemhut.com
The mining
of Tanzanite is no easy job with many obstacles stand in the way. Using
outdated techniques miners spend the whole day in the mines with little to show
at days end. The Rainy seasons creates flooding in the mines slowing down the
mining of the gemstones even more. Flooding also causes untimely deaths of the
miners. The mines are broken down into four active blocks lettering A through
D. Some of the blocks are well known. Blocks A and C are reserved for foreign
investment. The C block produced the largest crystal in the world and is the
largest producer of Tanzanite out of all the blocks. D block produces the best
quality and color of tanzanite. Gems TV refers to the Tanzanite from the D
block as “AAA- Tanzanite”.
Left, is the worlds largest crystal found 16,839 carats and measures 22cm at its’ widest point. Both Photos show largest single rough stones found to date.(Gemstones & Jewelry)
Photos © - Tanzanite One Ltd. Lay out of C block
Tanzanite
is a blueish-purple gemstone variety of the mineral zoisite, which is a calcium
aluminium hydroxy
sorosilicate belonging to the epidote group of
minerals. Tanzanite has a hardness of 6 to 6 1/2 on the
Mohs scale. The
Toughness of Tanzanite is Poor to Fair. Tanzanite
is in the
orthorhombic crystal system, with a "bladed"
crystal habit. Tanzanite has a
refractive index of 1.691. (Gemstones & Jewelry)
Fun
Facts of Tanzanite
- Tanzanite was used in the movie Titanic for coveted blue jewel
- 2002 Tanzanite was added to Decembers birthstone (which was the first time the list has changed since 1912)
- Masai chief gave Tanzanite to wives on the birth of their children. Today the gem is given to mothers on the birth of their first child.
Sources
Gavin Linsell. Guides to Gems & Jewelry. Published by Gems TV holding Limited. www.gemstv.com
Gems hut. http://.gemhut.com
Diamonds & Gemstones. www.khulsey.com/jewlry/gemstones_tanzanite.html
“Something new about Tanzanite”. Swala Gem Traders. www.swalagemtraders.com
