Glossary Term
By Dr. Elif Demir Mineralogy Editor
The ratio of the speed of light in a vacuum to the speed of light in a given material. In gemology, refractive index is one of the primary identification tools, measured on a refractometer at the sodium D line (589 nm). Diaspore has a refractive index range of 1.682–1.752 with strong birefringence of ~0.048.
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