Diamond dust is a ground-level cloud composed of tiny ice crystals.This meteorological phenomenon is also referred to simply as icecrystals and is reported in the METAR code as IC. Diamond dustgenerally forms under otherwise clear or nearly clear skies, so it issometimes referred to as clear-sky precipitation. It is most commonlyobserved in Antarctica and the Arctic, but it can occur anywhere with atemperature well below freezing. In Polar regions diamond dust maycontinue for several days without interruption.
http://en.wikipedia.org/wiki/Diamond_dust
http://en.wikipedia.org/wiki/Diamond_dust
