Pleochroism = "Many Colored".
Reflected light microscopy is used to examine opaque minerals (and other materials, e.g.. ceramics) to determine the paragenetic relationships between different mineral phases and their identification. Often, the same specimen which is viewed using the light microscope can be analyzed using advanced x-ray and ion microprobe techniques.
The sample (polished thin section, epoxy grain mount, or polished section) is placed in the appropriate reflected light microscope. Pleochroism is an optical effect where the mineral appears to change colors as it is rotated while illuminated by plane polarized light. The polarizers are not crossed to observe pleochroism.
Isotropic minerals (eg, galena, pyrite) do not show any pleochroism when rotated in plane polarized light. Minerals which are pleochroic are also bireflectant. Care must be taken when observing pleochroism to follow these rules:
Other References to Pleochroism
An Atlas of Opaque and Ore Minerals and their Associations from the SME
Reflected-light Microscopy from the University of Utah.
Data from the "Visible Light Spectrum" program from efg's Computer Lab was used to obtain the spectral colors used in the calculation of the macroscopic color based on reflectance measurements.
Dan Bruton's COLOR SCIENCE web page.
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