Opaline

Opaline is an adjective meaning opal-like or possessing the milky, iridescent appearance characteristic of opal. The term is used to describe materials that exhibit opalescence—the soft glow and play of color produced by light scattering within a translucent medium.

In glassmaking, opaline glass or opaline refers to a class of glass with a cloudy, milky look resulting from microscopic particles or phase separation that scatter light. This produces a pearly, shimmering surface and is found in decorative wares and tableware. Opaline glass has appeared in many cultures and periods, with methods including opacification via additives and controlled crystallization.

In geology and mineralogy, opaline describes silica-rich substances that are opal-like in structure or appearance. This includes opaline silica and other hydrated silica materials that lack a defined crystal lattice. The term is used to distinguish these amorphous or microcrystalline forms from vitreous quartz or chalcedony.

Etymology: the term derives from opal, with the suffix -ine forming an adjective.

See also: opal, opalescence, opaline silica.