Diamond dust is a ground-level
cloud composed of tiny
ice crystals. This
meteorological phenomenon is also referred to simply as
ice crystals and is reported in the
METAR code as IC. Diamond dust generally forms under otherwise clear or nearly clear skies, so it is sometimes referred to as clear-sky
precipitation. It is most commonly observed in
Antarctica and the
Arctic, but it can occur anywhere with a temperature well below freezing. In
polar regions diamond dust may continue for several days without interruption.