playofcolor

Play of color, or play-of-color, is an optical phenomenon most closely associated with precious opal. It describes the flashing spectral colors displayed by the stone as light diffracts through its internal microstructure and the viewing angle changes. Common opal may lack this color play, showing mainly body color rather than bright color flashes.

The effect arises from opal’s unique composition. It consists of tiny silica spheres, typically 150–300 nanometers in diameter, packed in a regular lattice. When white light enters the stone, it is diffracted by this orderly arrangement, producing constructive interference at specific wavelengths and a spectrum of colors. The visible colors depend on sphere size and packing, as well as the stone’s hydration and the geometry of light and observation.

Colors may appear as broad flashes or as discrete patches called patterns. Popular patterns include harlequin and ribbon. The contrast against the body color and the opal’s transparency influence perceived brightness and value; dark or black opals with strong play of color are generally more prized.

Formation and care are also noted. Precious opal forms when silica-rich solutions fill voids in sedimentary rocks, with water content typically around 3–21%. Dehydration or rough handling can dull the color play. Opal is relatively soft (Mohs 5.5–6.5) and sensitive to heat, solvents, and impact, so gentle cleaning and storage are advised.

Other minerals can exhibit iridescence that resembles play of color, such as labradorite’s labradorescence, but these effects are described with different terms and not as play of color.