Editing Diamond dust (section)

==Formation==
[[Image:Sun halo optical phenomenon edit.jpg|thumb|upright|Halo display at the South Pole (1980), featuring a [[parhelion]], [[22° halo]], [[parhelic circle]], [[upper tangent arc]] and [[Parry arc]]. Diamond dust is visible as point-like reflections of individual crystals close to the camera.]][[File:Losvåttån Løkken Verk 2.jpg|thumb|Diamond dust in [[Løkken Verk]], Norway.]]
These ice crystals usually form when a [[Inversion (meteorology)|temperature inversion]] is present at the surface and the warmer air above the ground mixes with the colder air near the surface.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|author=Glossary of Meteorology|date=June 2000|title=Diamond Dust|publisher=[[American Meteorological Society]]|access-date=2010-01-21|url-status=dead|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=2009-04-03}}</ref> Since warmer air frequently contains more [[water vapor]] than colder air, this mixing will usually also transport water vapor into the air near the surface, causing the [[relative humidity]] of the near-surface air to increase. If the relative humidity increase near the surface is large enough then ice crystals may form.

To form diamond dust the temperature must be below the [[Melting point|freezing point]] of water, {{convert|0|C|abbr=on}}, or the ice cannot form or would melt. However, diamond dust is not often observed at temperatures near {{convert|0|C|abbr=on}}. At temperatures between {{convert|0|C|abbr=on}} and about {{convert|-39|C|abbr=on}} increasing the relative humidity can cause either fog or diamond dust. This is because very small droplets of water can remain liquid well below the freezing point, a state known as [[Supercooling|supercooled]] water. In areas with a lot of small particles in the air, from human pollution or natural sources like dust, the water droplets are likely to be able to freeze at a temperature around {{convert|-10|C|abbr=on}}, but in very clean areas, where there are no particles ([[Ice nucleus|ice nuclei]]) to help the droplets freeze, they can remain liquid to {{convert|-39|C|abbr=on}}, at which point even very tiny, pure water droplets will freeze. In the interior of Antarctica diamond dust is fairly common at temperatures below about {{convert|-25|C|abbr=on}}.

Artificial diamond dust can form from snow machines which blow ice crystals into the air. These are found at ski resorts. Diamond dust may also be observed immediately downwind from manufacturing facilities or chilled water plants that produce steam.