Cause of Color :
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.
Crystal inclusions, liquid tubes.
Optic Character :
Anisotropic, D.R.; Biaxial positive or negative (depends on wavelengths of light used)
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)
Myanmar, Japan, Madagascar, Russia, Mexico.
Specific Tests :
Slowly attacked by hydrochloric acid.
Sometimes shows line at 580nm (didymium lines – rare earth spectrum).