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Danburite


Properties
Chemical Composition: 
Borosilicate of calcium - CaB2(SiO4)2
Classification / Type: 
-
Colors / Varieties: 
Colorless, white, pink, light to dark yellow, yellowish brown, brown.
Crystal System / Forms: 
Orthorhombic System / Prismatic and wedge shaped crystals are common.
Hardness: 
7
Specific Gravity: 
3.00
Cleavage / Fracture: 
None / Uneven Fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial positive or negative (depends on wavelengths of light used)
Lustre: 
Vitreous.
Refractive Index / Birefringence: 
1.630 - 1.636 / 0.006
Pleochroism: 
Weak to none.
Dispersion: 
0.017
Magnification: 
Crystal inclusions, liquid tubes.
U.V. Fluorescence: 
Sky blue to bright blue-green in longwave. Thermo-luminescent: reddish tint when heated. (Phosphoresces)
Spectrum: 
Sometimes shows line at 580nm (didymium lines - rare earth spectrum).
Cause of Color: 
Color center.
Treatment (Enhancement): 
-
Specific Tests & Remarks: 
Slowly attacked by hydrochloric acid.
Synthesis: 
-
Simulants (with key separation tests): 
Topaz (S.G.), Andalusite (pleochroism), Beryl (optic figure, R.I., S.G., inclusions), Quartz (optic figure, R.I., S.G.), Tourmaline (optic figure, R.I., birefringence, inclusions)
Geological Occurrence: 
In carbonate veins in granite rocks.
Sources: 
Myanmar, Japan, Madagascar, Russia, Mexico.
Cuts & Uses: 
Facetted, cabochon, etc.
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