Photo of Tanzanite in Processed & Rough Form
Tanzanite is a mineral with a hardness of 6 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhombicly structured gems are made of calcium aluminum silicate hydroxide, their full chemical compound being Ca2Al3(SiO4)(Si2O7)O(OH).
Tanzanite is something of bluish to violet variety of zoisite, that wasnt discovered until 1967 believe it or not. It was first found in the Mererani Hills of northern Tanzania. Tanzanite has strong trichroism, appearing alternately blue, violet, or burgundy depending on the crystal orientation and lighting conditions.
Most tanzanite is heat-treated to enhance the color, and natural tanzanite seems to contain more brownish pigments that are not really associated with a quality stone.
What mechanisms create Tanzanite's trichroic effect?
The complex trichroic pleochroism results from structural orientation of vanadium and chromium within the crystal lattice, displaying blue, violet, and burgundy colors along different crystallographic axes when heated.
How does heat treatment affect crystallographic structure?
Heat treatment at 500-600°C modifies vanadium oxidation states, transforming brown zoisite to blue-violet tanzanite. This process alters electron configuration without changing basic crystal structure.
What geological conditions restrict formation?
Formation requires specific regional metamorphism conditions with vanadium-rich environment, explaining its unique occurrence in the Merelani Hills. Local tectonics and geochemistry create conditions unreplicated elsewhere.
How is crystal orientation determined for optimal color?
Crystallographic orientation during cutting maximizes the blue-violet pleochroic direction. The c-axis typically provides optimal face-up color, requiring precise orientation during faceting.
What causes color zoning in natural specimens?
Color zoning results from varying vanadium and chromium concentrations during crystal growth. Zoning patterns often follow crystallographic planes, providing insight into formation conditions.
How do inclusions affect treatment efficacy?
Specific inclusion types can affect heat treatment results. Stress-induced fractures and graphite inclusions may influence color development and overall treatment success.
What analytical methods quantify color saturation?
UV-Vis-NIR spectroscopy measures absorption characteristics. Quantitative color analysis uses standardized colorimetric parameters to evaluate treatment effectiveness and color quality.
The specific gravity [?] for Tanzanite is 3.35, its refractive index [?] is 1.69-1.70, and its double refraction [?] is 0.009.
History
Tanzanite was named after Tanzania, the country where it was found, that statement might be self explanatory. Tiffany and Co first introduced it to the market in 1968, promoting it as an exotic gemstone. In recent years tanzanite has gained immense popularity and was added as an alternative December birthstone by the American Gem Trade Association in 2002.
Industrial Usages
Tanzanite is currently too rare to have any known industrial applications.
You May Also Like...
Zoisite: Zoisite is a hydrous calcium aluminum silicate in the Epidote group, with an orthorhombic crystal system, three crystal axes at right angles to each other, all of varying lengths. It appears in elongated, prismatic crystals, with fine parallel lines on the prism faces and usually poorly terminated. It also appears frequently in formless grains, poorly-defined crystals, rodlike aggregates and gran (read full)
Benitoite: Benitoite is a rare gemstone / mineral that fluoresces when lit by black lights. It gets its name from San Benito County, California where it was first found. This gem is almost always blue (it was originally thought to be a sapphire) but also has variations in purple, pink, and clear. Gem prices seem to fluctuate but a few hundred dollars per half ct is common. Why so expensive? The quality gem (read full)
Sapphire: Sapphire is the blue variety of Corundum. Sapphires can be a very dark blue, to the point of seeming dense and blackish from a distance, sometimes accompanied by a blue to dull green pleochroism, which is only visible from the side in cut stones. They may also be a strong, but not too bright blue, easily recognizable from a distance, this being the real color. Other possibilities are light, usual (read full)
