Spinel – Lab-made, Faceted, Blue

Spinel is singly refractive. However, a synthetic spinel may show anomalous double refraction (ADR). Testing gemstone refraction with a polariscope can identify ADR. Silver pendant with synthetic spinel. Photo by gosiko. Licensed under CC By-SA 3.0.

Article: Polariscope Guide, Part 1: Testing Gemstone Refraction

Credit: gosiko