English: Single crystals These remarkably uniform and large ice crystals were found by the Afon Ystwyth, near Grogwynion. They are single crystals, meaning that each of them has a uniform crystal structure and orientation throughout, rather than consisting of many independently crystallised domains: A water molecule at one end of one of these about 8mm long rods is orientated exactly the same as one at the other end, with about 40 million identically aligned other water molecules in between! Such single crystal growth occurs only if there is a shortage of crystal nuclei and it takes a long time - clean air and a cold spell of several days. The fact that the crystals are all about the same size suggests that nucleation occurred at the same time for all of them - the temperature must have dropped well below freezing rather quickly at the beginning of the cold spell.