Wikipedia:POTD column/September 26, 2006

Scanning electron micrograph of a capped column snowflake, with rime frost, a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects, on both ends. When the riming process continues so that the shape of the original snow crystal is no longer identifiable, the resulting crystal is referred to as graupel.

Photo credit: Eric Erbe and Chris Pooley, USDA
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