GEMSTONE LIBRARY
TOPAZ
Topaz is a colourless, yellow, orange, pink or blue gem. The rose-orange variety is the most sought after (imperial topaz). Topaz is a fragile gem with clean basal cleavage but its high hardness makes it a highly appreciated gem.
Each gemstone brought to the laboratory is analysed and identified. In the case of topazes, coating treatments are identified but irradiation or heating treatments are very difficult to detect.
CHARACTERISTICS
- Name: Topaz
- Mineralogical nature: Topaz
- Colour: Colourless, yellow, orange, pink, blue, pink-orange (imperial topaz)
- Crystal system: Orthorhombic
- Chemical composition: Al2(SiO4)(F, OH)2
- Causes of colour: Coloured centres, Cr3+
- Density: 3.52 to 3.56
- Hardness: 8
- Cleavage: Clean basal {001}
- Fracture: Irregular, subconchoidal
- Optic sign: Positive bias
- Refractive index: np: 1.608 to 1.629 / nm: 1.609 to 1.631 / ng: 1.616 to 1.640
- Birefringence: 0.007 to 0.009
- Dispersion: 0.014
- Pleochroism: Low, more or less visible to the eye depending on the colour
- UVL: Yellow, green or weak blue depending on the fluoride content
- UVC: Same but weaker than UVL
- Treatments: Thermal treatment
- Irradiation
- Syntheses: In a research laboratory
- Geographical origin: Brazil, Madagascar, Russia, Sri Lanka, etc.
CONTACT US :
contact@lfg.paris
(+33) 01 40 26 25 45
30, rue de la Victoire - 75009 Paris
Monday - Thusday : 9H30 to 17H00
Friday : 9h30 to 16h30
Withdrawal files at same days and time
