Ice crystals formed when water vapor from the atmosphere condenses directly into the solid phase onto a very cold surface. The process is the equivalent of dew. These crystals generally form during cold and clear conditions, particularly at night. Surface Hoar crystals (or just Hoar Crystals) grow in flat plates, and once they are buried they have very little strength. They also collapse into a very thin layer which can be difficult to identify and/or assess the strength of.
Deposition of water vapor from the air as ice crystals on to a cold surface (e.g., a snow surface).
the deposition (sublimation) of ice crystals on a surface which occurs when the temperature of the surface is colder than the air above and colder than the frost point of that air