I recently went ahead and freezed - heated - freezed - heated a giant laggy room of water, when all of a sudden during a freeze I noticed there was another particle I did not know - RIME

I searched through the collection of particles but could not find it.. could someone explain to me what this is and what this does?
http://s398.photobucket.com/albums/pp61/Lunialfakemon/?action=view&current=RIME.png

geerly
how do I not-screw the pic?

Cool, thanks