It's because heavy powders produce a tiny amount of pressure,not because of magic rocks
you added pressure that's why
It is really true i put the plutonum in rock and it exploded too
Its not the rock, nor is it newtonian gravity, its just the fact that plutonium starts undergoing nuclear fission in high quantities, reacting and making neutrons, causing a nuclear reaction. Nothing is wrong with it and no neutrons in there, just the amount of plutonium being too high.
and it looks like you spent more time on the SIGNS that the save itself because it's messy and uncreative.
Seriously? It's exploding because you put neut in there.