Rocks will crack for two reasons when boiling:
1.. Gas will generate inside the rock and if the pressure cannot dissipate then the rock will crack.
2..If heated too quickly there will be thermal growth on the outside of the rock before the inside, the rock will most likely crack depending on its structure.
Either way, be careful.
1.. Gas will generate inside the rock and if the pressure cannot dissipate then the rock will crack.
2..If heated too quickly there will be thermal growth on the outside of the rock before the inside, the rock will most likely crack depending on its structure.
Either way, be careful.