Interference colour chart

An interference colour chart, first developed by Auguste Michel-Lévy, is an optical mineralogy tool to identify minerals in thin section using a petrographic microscope. With a known thickness of the thin section, minerals have specific and predictable colours in cross-polarized light, and this chart can help identify minerals. The colours are produced by the difference in speed in the fast and slow rays, also known as birefringence.

When using the chart, it is important to remember these tips:

• Isotropic and opaque (metallic) minerals cannot be identified this way.
• Rotate the stage in order to get the maximum colour, and therefore, the maximum birefringence.
• Each mineral, depending on the orientation, may not exhibit the maximum birefringence. It is important to try and find multiple like minerals in order to get the best value of birefringence.
• Uniaxial minerals can look isotropic (always extinct) if the mineral is cut perpendicular to the optic axis. (But this situation can be revealed with the Conoscopic interference pattern).

References

• Nesse, W. D., 1991, Introduction of Optical Mineralogy, 2nd edition.

External links

• Example chart from Webmineral
• Interactive Java-based interference color chart