One year ago today, it was very cold outside, 1° F to be precise (-17° C). These are the patterns of the ice crystals on our side window. The window is in a little, unheated arctic-type entryway, which we use mostly for storage and for taking off our muddy, wet, or icy boots so we can heat them on propane boot-heaters.
So far, the coldest temp I've seen in the morning has been about 15° F (-9° C), and most mornings have been between 25 and 30 F (-4 to -1 C).
Remember, ice is a mineral, and here it's showing off its crystalline nature.