Pleochroism


Pleochroism

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.

Pleochroism is caused by the double refraction of light by a colored gem or crystal. Light of different polarizations is bent different amounts by the crystal, and therefore follows different paths through the crystal. 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. 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. In such cases, a thin section of the mineral is used and examined under polarized transmitted light in a microscope.

ee also

* Birefringence


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  • Pleochroism — Ple*och ro*ism, n. [Gr.? mor? + ? color.] (Crystallog.) The property possessed by some crystals, of showing different colors when viewed in the direction of different axes. [1913 Webster] …   The Collaborative International Dictionary of English

  • pleochroism — [plē äk′rō iz΄əm] n. [< PLEO + Gr chrōs, color (see CHROOUS) + ISM] the property of some minerals of absorbing selectively various wavelengths of light and of displaying different colors when looked at in the directions of the different… …   English World dictionary

  • pleochroism — /plee ok roh iz euhm/, n. the property of certain crystals of exhibiting different colors when viewed from different directions under transmitted light. Cf. dichroism (def. 1), trichroism. [1855 60; PLEOCHRO(IC) + ISM] * * * ▪ optics  (from Greek …   Universalium

  • pleochroism — pleochroizmas statusas T sritis chemija apibrėžtis Medžiagos spalvos priklausomybė nuo šviesos bangų sklidimo krypties ir poliarizacijos. atitikmenys: angl. pleochroism; pleochromatism; polychroism; polychromatism rus. плеохроизм …   Chemijos terminų aiškinamasis žodynas

  • pleochroism — kristalų daugiaspalviškumas statusas T sritis fizika atitikmenys: angl. pleochroism; pleochromatism; polychroism vok. Pleochroismus, m; Polychroismus, m rus. плеохроизм, m pranc. pléochroïsme, m; polychroïsme, m …   Fizikos terminų žodynas

  • pleochroism — noun the phenomenon of different colors appearing when certain crystals are viewed from different directions • Hypernyms: ↑optical phenomenon • Hyponyms: ↑dichroism, ↑trichroism * * * plēˈäkrəˌwizəm noun ( s) …   Useful english dictionary

  • pleochroism — noun Etymology: International Scientific Vocabulary pleochroic, from pleio + Greek chrōs skin, color Date: 1857 the property of a crystal of showing different colors when viewed by light polarized in different directions • pleochroic adjective …   New Collegiate Dictionary

  • pleochroism — noun the optical phenomenon in some coloured, transparent crystals (such as tourmaline) in which the colour is different in different directions See Also: dichroism, trichroism …   Wiktionary

  • pleochroism — SYN: pleochromatism. * * * ple·och·ro·ism plē äk rə .wiz əm n the property of a crystal of showing different colors when viewed by light that vibrates parallel to different axes pleo·chro·ic .plē ə krō ik adj * * * pleo·chro·ism (pleґo… …   Medical dictionary

  • pleochroism —    The property exhibited by double refracting colored crystals of showing different colors when the transmitted light is viewed along different axes. The color depends on the orientation of the substance and arises because of differential… …   Forensic science glossary


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