Reflected Light Color

See Also: Reflectivity, Pleochroism, Bireflectance, and Anisotrophism.

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. Color is observed using plane polarized light with the appropriate illumination level.

The sample's color is, at best, fairly characteristic of the particular mineral. Care must be taken when comparing colors to follow these rules:

Sample is freshly polished and does not have any tarnish.
Illumination level is not too excessive (intensity changes the color balance).
Samples of known minerals are available for comparison.
Plane polarized light provides some indication of anisotropism in non-isotropic minerals.
Colors appear to be changed by having other minerals in the field of view.

The following example shows the subjective effect of having the same "mineral" surrounded by a "mineral" of a different color.

Identical Yellow Square on Right Appears "Yellower"

Other References to Reflectivity and "Color"

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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Example Subject Searches

Example: "RL Color" finds all minerals that have reflected light color data.
Example: "short uv-yellow*" finds all minerals that are fluorescent yellow in the short ultra violet.