Definition: Diamond dust: Precipitation that falls from a clear sky in very small ice crystals, often so tiny that they appear to be suspended in the air.
Diamond dust can be observed in polar and alpine regions and continental interiors, especially in clear, calm and cold weather. It forms at temperatures typically less than –10 °C in a rapidly cooling airmass. Diamond dust is usually composed of well-developed crystals (often plates), with typical diameters of about 100 μm.
These crystals, which are visible mainly when they sparkle in the sunlight, can also produce halo phenomena.
Visibility in diamond dust varies considerably, and the lower limit is greater than 1 km.