Crystals AE when they hit the walls. Big one = 100 range, Middle size = 50 range, small = 25 or something like that. Big one = 15k nuke, Middle = 7.5, small = 3250ish.
Big crystal falls (not sure if it AEs when it hits ground - dont think it does), then it starts to move...it hits back wall, 15k 100' AE and splits in two, those two go back to other wall, 7.5k 50' AE and splits in two (to make 4 total), those 4 roam back to hit the wall again to let off a 3.25k 25' AE.
I'm not 100% sure if it nukes when it falls or not - I have no evidence to say it does but it very well may. I know for sure they nuke each time when they hit the wall if you're nearby.
This could all be wrong - but per logs it looks like this is the case.