Pleochroism is an optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a petrographic microscope. An optical phenomenon is any observable event which results from the interaction of Light and Matter. A petrographic microscope is a Microscope used in Petrology and Optical mineralogy to identify rocks and Minerals in Thin sections

Pleochorism is caused by the double refraction of light by a colored gem or crystal. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Light of different polarizations is bent different amounts by the crystal, and therefore follows different paths through the crystal. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations The components of a divided light beam follow different paths within the stone and travel at different speeds, and each path will absorb different colors of light. When the stone is observed at some angle, light following some combination of paths and polarizations will be present, each of which will have had light of different colors absorbed. At another angle, the light passing through the stone will be composed of another combination of light paths and polarizations, each with their own color. The light passing through the stone will therefore have different colors when it is viewed from different angles, making the stone seem to be of different colors.

Some stones show two colors or shades and are called dichroic. Dichroic redirects here For the filter see Dichroic filter. For the glass see Dichroic glass. Some show three and are trichroic. Gems are sometimes cut and set either to display pleochroism or to hide it, depending on the colors and their attractiveness.

Pleochroism is an extremely useful tool in mineralogy for mineral identification, since minerals that are otherwise very similar often have very different pleochroic color schemes. Mineralogy is an Earth Science focused around the Chemistry, Crystal structure, and physical (including optical) properties of Minerals A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific In such cases, a thin section of the mineral is used and examined under polarized transmitted light in a microscope. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are

See also

• Birefringence

Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray

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