Pleochroism

Part of speech: noun

Definitions

1. the optical property of certain crystals or minerals to display different colors when viewed from different directions or under varying light conditions
2. a crystallographic characteristic where a material exhibits multiple distinct hues depending on the angle of observation and the polarization of transmitted light
3. the phenomenon in which a mineral or gemstone appears to change color based on the viewing direction due to selective absorption of light waves along different crystal axes

Etymology: Pleochroism is built from Greek roots: "pleon" meaning "more," and "chroos" meaning "colour" (or skin, complexion), with the suffix "-ism" added to name a property. The term was coined in the 19th century for a specific optical behaviour of certain crystals, which can show different colours when viewed along different crystal axes under transmitted light. The Greek "pleochroos" was not a word anyone used for minerals; the modern scientific sense was built from these classical parts. The word was formed in the context of mineralogy, where crystal optics was being studied closely. Early observers noticed that a tourmaline crystal, for example, could look green along one direction and brown along another, and a physical explanation for this emerged from the study of light absorption in anisotropic crystals. Naming the phenomenon in one compact term let scientists refer to it without describing the whole effect each time.