Variety of prismatic colors seen in rapid succession. A phenomenon seen in opal, fire agate, and other similar stones caused by the interference and diffraction of light.
The way in which colors change as an opal is tilted in different directions. Play of color in an opal, (its "flashes" or "fire") is caused by light interference patterns created by the tiny spheres that make up opal's structure. These spheres are about 0.001 millimeters in diameter
This is flashes of rainbow colors in Opal that change with the angle of observation. This should not be confused with “opalescence”, which is the milky blue or pearly appearance of Opal caused by the reflection of light.