Tanzanite
Tanzanite was discovered in the Meralani Hills of Tanzania, East Africa in the 1960's. It has a colour range of light violet, to blue, to deep purple and strong trichroic pleochroism. So that deep blue stones appear purple when turned and flashes of red or yellow may appear through the facets. Intense colours rarely occur naturally, most highly saturated tanzanite is produced by heat-treatment. The heat treatment process produces gemstones of outstanding colour and intensity. There is a limited supply of Tanzanite and the only known deposit is currently in Tanzania.
Source location for tanzanite: Tanzania is the only known deposit.
Properties of the Gemstone and Additional Information
| Gemstone type: | Tanzanite is a variety of zoisite. |
| Crystal System: | Orthorhombic |
| Chemical Composition: | Calcium aluminium silicate, Ca2Al3(SiO4)3(OH) |
| Colour: | Light violet, blue to a deep rich purple. |
| Lustre: | Vitreous |
| Pleochroism: | Trichroic strong: Purple, blue and greenish to brownish yellow. |
| Dispersion: | Low |
| Hardness: | 6 1/2 on the Mohs' scale. |
| Toughness: | Poor |
| Cleavage: | Perfect |
| Density in gm/cc: | 3.15 to 3.38 |
| Double refraction: | Yes |
| Refractive index: | 1.69 to 1.70 |
Common Treatments
Stones are usually heat-treated to improve the colour, undesirable yellow and brown tints are removed during this process.
Brown stones are heat-treated to produce intense blue coloured stones.