What is the common term for the brilliant colors exhibited by opal when viewed from different angles?

The term "play-of-color" specifically refers to the unique optical phenomenon seen in opals, characterized by the vibrant and shifting colors that can be observed when the stone is viewed from different angles. This effect arises from the microstructure of opal, which consists of tiny silica spheres arranged in a specific pattern. When light enters the opal, it is refracted, and different wavelengths are separated, creating a spectrum of colors that change with the angle of observation. This quality makes opal distinct from other gemstones and is a key feature that enhances its appeal.

Other terms like "color shift," "opalescence," and "interference color" refer to different phenomena or optical effects that do not precisely describe the visual quality of opal. While "color shift" might suggest a change in color due to lighting or other conditions, it does not capture the essence of the variable color display unique to opal. "Opalescence" is often associated with the milky or cloudy appearance of some opals, but it does not encompass the full vibrancy of the play-of-color effect. "Interference color" refers to the hues seen due to the interference of light waves, which is a broader optical phenomenon that applies to various materials and is