Tanzanite

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Tanzania
9.90 carats
© Palagems

Tanzanite is called after the East African state of Tanzania, it was discovered in the Mererani Hills of Northern Tanzania in 1967.

Tanzanite is the blue-purple variety of Zoisite, it is noted for its remarkably strong trichroism, appearing sapphire blue, violet and burgundy depending on the position of crystal. Tanzanite also appears differently when viewed under alternate lighting conditions. In good quality the colour is ultramarine to sapphire blue; in artificial light, it appears more amethyst violet.

Tanzanite is universally heat treated to produce a range of hues between bluish-violet to violetish-blue, it has no effect on price.

Tanzanite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 
 
 
 

Tanzanite Gemstones by Size

This table shows distribution of Tanzanite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.20 cts
Heaviest:15 cts
Average:3.17 cts
Total photos:65
Do you have a larger Tanzanite? Why not upload a photo?
0.20ct to 1.68ct1.68ct to 3.16ct3.16ct to 4.64ct4.64ct to 6.12ct6.12ct to 7.60ct7.60ct to 9.08ct9.08ct to 10.56ct10.56ct to 12.04ct12.04ct to 13.52ct13.52ct to 15.00ct
General Information
A variety or type of:Zoisite
Chemical Formula
Ca
 
2
Al
 
3
(SiO
 
4
)
 
3
(OH)
Walter Schumann, Gemstones of the world (2001)
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Photos of natural/un-cut material from mindat.org
Tanzanite Treatments
When heated to 752 - 932 degrees F (400 - 500 degrees C), the interfering yellowish and brown tints vanish, and the blue becomes deeper. - Gemstones of the world, Walter Schumann, 2001, p 160
Tanzanite Simulants
There are glass imitations and doublets made from glass with tanzanite crown or made from two colourless synthetic spinels glued with tanzanite-coloured glue. - Gemstones of the world, Walter Schumann, 2001, p 160
Physical Properties of Tanzanite
Mohs Hardness6.5 to 7
Walter Schumann, Gemstones of the world (2001)
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Specific Gravity3.35
Walter Schumann, Gemstones of the world (2001)
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TenacityBrittle
Michael O’Donoghue, Gems, Sixth Edition (2006)
Cleavage QualityPerfect
Walter Schumann, Gemstones of the world (2001)
FractureUneven
Walter Schumann, Gemstones of the world (2001)
Optical Properties of Tanzanite
Refractive Index1.685 to 1.707
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterBiaxial/+
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.006 to 0.013
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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PleochroismViolet/purple stones - strong trichroism: strong blue - purple - greenish (to brownish) yellow; Blue stones - strong: strong blue - purple - greenish-yellow
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Dispersion0.030
Walter Schumann, Gemstones of the world (2001)
ChatoyancyYes
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Colour
Colour (General)Sapphire blue, amethyst, violet
Walter Schumann, Gemstones of the world (2001)
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Causes of ColourBlue, (heat treated), V4+ in octahedral coordination; with V3+ in octahedral coordination. Brown-violet, V3+ in octahedral coordination (treatment turns blue). Green, Cr3+ in octahedral coordination.
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Fluorescence & other light emissions
Fluorescence (General)Inert
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Fluorescence (Long-Wave UV)Rare bluish
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Crystallography of Tanzanite
Crystal SystemOrthorhombic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
HabitMultifaced prisms, mostly striated
Walter Schumann, Gemstones of the world (2001)
Geological Environment
Where found:Tanzanite occurs in calcareous rocks,
including metamorphosed dolomite and calcareous shales subjected to regional metamorphism.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Tanzanite information at mindat.org
Significant Gem Localities
Tanzania
 
  • Manyara Region
    • Simanjiro District
      • Lelatema Mts
        • Merelani Hills (Mererani)
Malisa (2003)
Malisa (2003)
Malisa (2003)
Malisa (2003)
Malisa (2003)
Malisa (2003)
Copyright © Jolyon & Katya Ralph 1993-2017. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.