Tourmaline Group
| Refractive Index : 1.644 – 1.624 + 0.134 – 0.021 |
| Optical Characteristic : DR U- |
| Specific Gravity : 3.06 + 0.20 – 0.06 |
| Formula : Na(Li,AI)3AI6(BO3)3Si6018(OH)4 |
| Crystal System : Trigonal |
| Variety/Species : All |
| Species/Group : Tourmaline Group |
| Birefringence : 0.018 to 0.040 |
| Dispersion : 0.017 |
| Hardness : 7 to 7.5 |
| Toughness : Fair |
| Ultrasonic : Risky |
| Steam : Risky |
| UV Long : Inert to weak |
| UV Short : Inert to moderate |
| Pleochroism : 2 colors |
| Strength : Weak to strong |
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| Pleochroism Colors : Press the |
| Heat : May fracture or change color |
| Acids : No reaction |
| Light : Stable |
| Polish Luster : Vitreous |
| Fracture : Conchoidal |
| Fracture Luster : Vitreous |
| Clarity Type : I to III |
| Tones : 2-8 |
| Saturations : 1-5 |
| Cause of Color : Varies:See variety |
| Enhancements : Heating, Irradiation, acid treatment |
| Cleavage : None |
| Color Range : Almost any color is possible. |
| Transparency : Transparent to Opaque |
| Phenomena : Color change, (rare), aventurescence, Chatoyancy |
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| Separations : Tourmaline Group from-
Topaz : birefringence, optic character, SG, cleavage, spectrum(possibly) Andalusite : birefrigence, optic character, pleochrosim, SG Peridot : RI, SG, birefringence, optic character, pleochrosim, spectrum Iolite : RI, SG, optic character, pleochroism |
| Identifying Characteristics and information
Thread-like liqiud and gas inclusions,gas filled fractures. |
| Spectral Data Not diagnostic. Weak spectra usually observed |
| Trade Names and Misnomers |
Tags: Trigonal
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