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Interference colour chart

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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 colors in cross-polarized light, and this chart can help identify minerals. The colors 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 do not apply.
  • Rotate the stage in order to get the maximum color, 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.

See also

Example chart from Webmineral

References

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

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