Ice crystals are a type of frozen water that form when temperatures drop below freezing. The two crossword solutions for the term 'ice crystals' are 'FROST' and 'HOARFROST'. FROST is a thin layer of ice that forms on surfaces when temperatures drop below freezing. HOARFROST is a type of FROST that forms when the air is humid and temperatures drop below freezing. It is characterized by white, feathery ice crystals that form on surfaces.