GEMSTONE LIBRARY
TANZANITE
Tanzanite is a blue to purple-blue variety of zoisite. This variety of zoisite is mined in Tanzania. The blue colour of the tanzanites can be achieved by heating brown-coloured zoisites.
Each gemstone brought to the laboratory is analysed and identified. With tanzanites, heat treatments can be detected, particularly through spectrometry.
CHARACTERISTICS
- Name: Tanzanite
- Mineralogical nature: Zoisite
- Colour: Blue to purple
- Crystal system: Orthorhombic
- Chemical composition: Ca2Al3Si3O12(OH)
- Causes of colour: V3+ and V4+
- Density: 3.23 to 3.38
- Hardness: 6 to 6,5
- Cleavage: Clean {100}
- Fracture: Conchoidal
- Optic sign: Positive bias
- Refractive index: np: 1.696 to 1.700 / nm: 1.696 to 1.702 / ng: 1.702 to 1.718
- Birefringence: 0.006 to 0.009
- Dispersion: 0.021
- Pleochroism: Strong yellow-brown to blue to purple
- UVL: Inert
- UVC: Inert
- Treatments: Thermal treatment
- Syntheses: In a research laboratory
- Geographical origin: Tanzania
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