Theory 12/Phase & ice/Snow crystals
Habit Is Diffusion Against Kinetics
The claim
Snow crystal habit is set by the ratio of vapour diffusion rate to surface attachment kinetics, which changes with temperature and produces plates at one range and needles at another.
01Mechanism
Fast attachment favours branching while slow attachment favours compact forms.
02Prediction
Habit should switch at temperatures where the ratio crosses one.
03Refutation
Habit fixed by humidity alone would remove kinetics.