Anomalous birefringence is peculiar to almost all diamonds (both natural and synthetic) and serves as an indirect diagnostic feature.

Anomalous birefringence in natural and synthetic diamonds

• Those diamonds showing strong anomalous birefringence (manifested as intense interference coloring) are, as a rule, natural, while weak anomalous birefringence is typical of synthetics.
• Patterns arising due to anomalous birefringence may serves as another diagnostic feature. In natural diamonds, these patterns consist of thin dashes intersecting with one another (in some directions, anomalous birefringence is manifested as mosaic interference coloring). A black cross pattern is typical of synthetics.

Recommended procedure for studying anomalous birefringence:

- Carefully clean the sample under study before starting the tests.
- Test the sample in accordance with the recommended procedure for working with a polariscope.
- Analyze the observed features using the description of anomalous birefringence in natural and synthetic diamonds.