Glossary Term
By Dr. Elif Demir Mineralogy Editor
The difference between the highest and lowest refractive indices of an anisotropic gemstone. High birefringence produces visible doubling of pavilion facet edges when the gem is examined through the table. Diaspore has a birefringence of approximately 0.048 — high enough to produce diagnostic doubling, distinguishing it from singly-refractive lookalikes.
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