Generally colourless, danburite crystals may also be yellow or pink. They form wedge-shaped prisms, much like the ones from colourless topaz but distinguishable by cleavage (poor in danburite, perfect in topaz) and specific gravity (lower in danburite).

First found in the town of Danbury, Connecticut (USA). Gem-quality danburite occurs in Burma, Mexico, Switzerland, Italy and Japan.

Cause of Color :

Color center.

Chemical Composition :

Borosilicate of calcium – CaB2(SiO4)2

Crystal System / Forms :

Orthorhombic System / Prismatic and wedge shaped crystals are common.

Cuts & Uses :

Facetted, cabochon, etc.

Dispersion : 0.017
Hardness : 7
Lustre : Vitreous.
Magnification :

Crystal inclusions, liquid tubes.

Optic Character :

Anisotropic, D.R.; Biaxial positive or negative (depends on wavelengths of light used)

Pleochroism : Weak to none.
Refractive Index / Birefringence :

1.630 – 1.636 / 0.006

Simulants (with 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)

Sources :

Myanmar, Japan, Madagascar, Russia, Mexico.

Specific Tests :

Slowly attacked by hydrochloric acid.

Spectrum :

Sometimes shows line at 580nm (didymium lines – rare earth spectrum).

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