Nacreous

Nacreous is an adjective with two common uses. It describes something possessing the pearly, iridescent appearance of nacre, the substance known as mother of pearl, and traces of the same glossy, multicolored sheen. The term derives from nacre, the iridescent inner layer of many mollusk shells.

In biology and materials science, nacreous materials refer to natural or synthetic substances that resemble nacre in structure and optical effect. Nacre is composed of microscopic aragonite platelets arranged in a brick-and-mortar-like lamellar architecture, bound by an organic matrix, which contributes to toughness and lightness. Nacreous materials are studied for biomimicry and are used in coatings, ceramics, and composites that aim to combine strength with light weight and resilience.

In atmospheric science, nacreous clouds describe a class of clouds formed in the lower stratosphere, also known as mother-of-pearl clouds. They appear as iridescent bands, often pinkish or greenish, at high latitudes and are commonly seen during twilight. Formation requires extremely cold temperatures well below −80 °C and a stable, humid stratosphere; ice crystals refract and interfere light to produce the distinctive iridescence. Nacreous clouds are most frequently observed in polar regions during winter, and their appearance can indicate specific atmospheric conditions in the stratosphere.