opalescent

Opalescent describes a surface or material that displays an opal-like play of color, with a milky or pearly base and a shifting iridescence. The term may refer to gemstones such as opals, as well as other substances that show a similar luminous sheen, including certain shells, mother-of-pearl, glass, and ceramics. Opalescence can vary from faint to vivid and may be more noticeable under particular lighting or angles.

Etymology and usage: The word derives from opal, the gemstone known for its milky body and color flashes, with the -escent suffix indicating a tendency to become or display a characteristic. It is used in mineralogy, gemstone descriptions, and materials science, as well as in literary or descriptive prose, to convey a soft, diffuse glow.

Optical basis: Opalescence arises from light scattering and interference within a material's microstructure. In natural opals, an array of silica spheres diffracts light to produce a spectrum of colors. In synthetic opalescent glass or resin, dispersed particles or phase-separated regions scatter shorter wavelengths, producing a hazy, glow-like effect even while the material remains translucent. The appearance can change with viewing angle and illumination.

Examples and notes: Opalescent appears in jewelry descriptions, in the characterization of certain minerals, and in decorative arts. The term is distinct from transparent or translucent without iridescence and from iridescent, which is often more vivid or metallic in color.