Ce sont des cristaux de glace formés en général en air clair par températures très froides et humides. ICE CRYSTALS - Precipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriformclouds, frost, and ice fog. Also, they produce optical phenomena such as halos, coronas, and sun pillars. May be called "diamond dust." It is reported as "IC" in an observation and on the METAR.