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
Sample is freshly polished and does not have any tarnish.
Illumination level is not too excessive (intensity changes the perceived
relative intensity effect).
Minerals which are pleochroic (non-isotropic minerals) are also
Bireflectance is better observed under oil.
Other References to Pleochroism
An Atlas of Opaque and Ore Minerals and their Associations from the