opalin

Opalin is a term used in mineralogy and gemology to describe a type of opal that is milky or opaque, often exhibiting a play of color. Unlike precious opal, which is characterized by its transparent or translucent quality and iridescent flashes, opalin is less transparent and its colors may appear more diffused or clouded. The term is sometimes used interchangeably with milky opal or common opal, though distinctions can be subtle.

The appearance of opalin is due to the way light interacts with the internal structure of the opal. In opalin, the silica spheres that form the opal are larger or arranged in a less ordered fashion, causing light to scatter rather than diffract. This scattering results in a milky or cloudy background, on which any present play of color is less vivid and more subdued. While it may not possess the striking brilliance of precious opal, opalin can still be attractive and is often used in jewelry, especially when it exhibits subtle color variations.

The composition of opalin is hydrated amorphous silica, similar to other opals. Its geological formation typically occurs in sedimentary or volcanic environments. The specific color of opalin can vary widely, ranging from white and pale blue to yellow, pink, and even darker shades, depending on the presence of impurities. While it is generally considered less valuable than precious opal, its unique aesthetic qualities ensure its continued use and appreciation in the world of gemstones.