Ice-crystal haze

From Glossary of Meteorology

ice-crystal haze

A type of very light ice fog composed only of ice crystals (no droxtals), and at times observable to altitudes as great as 7000 m.

It is usually associated with precipitation of ice crystals. Observed from the ground, ice-crystal haze may be dense enough to hinder observation of celestial bodies, sometimes even the sun. Looking down from the air, however, the ground is usually visible and the horizon only blurred. For very sparse ice-crystal haze during daytime, sunlight reflecting from crystal faces produces sparkling in the air; hence the name diamond dust for these crystals.
Compare arctic mist.