[plee-ok-roh-iz-uh
m] 
| the property of certain crystals of exhibiting different colors when viewed from different directions under transmitted light. Compare dichroism (def. 1), trichroism. |
| ple·och·ro·ism (plē-ŏk'rō-ĭz'əm) n. The property possessed by some crystals of exhibiting different colors, especially three different colors, when viewed along different axes. [pleo- + Greek khrōs, color + -ism.] ple'o·chro'ic (plē'ə-krō'ĭk) adj. |
pleochroism
(from Greek pleion, "more," and chros, "colour"), in optics, the selective absorption in crystals of light vibrating in different planes. Pleochroism is the general term for both dichroism, which is found in uniaxial crystals (crystals with a single optic axis), and trichroism, found in biaxial crystals (two optic axes). It can be observed only in coloured, doubly refracting crystals. When ordinary light is incident on a crystal exhibiting double refraction, the light is split into two polarized components, an ordinary ray and an extraordinary ray, vibrating in mutually perpendicular planes. A dichroic substance such as tourmaline transmits only the extraordinary ray, having absorbed the ordinary ray (see ).
Learn more about pleochroism with a free trial on Britannica.com.