Nacreous clouds, or ice polar stratospheric clouds, are a rare type of cloud that forms in very cold conditions and at high altitudes.
They are known for their iridescent colors, which are created when sunlight interacts with the tiny ice crystals they are made of, according to the World Meteorological Organization (WMO). The name "nacreous" comes from "nacre," another name for mother-of-pearl, which refers to their iridescent appearance. They are sometimes called mother-of-pearl clouds.
