It wasn't a lined reservoir which may have lent it susceptible to corrosion.

Thanks for the commentary, you may be onto something.

: I will bet that there is a 98% chance that it was an American Standard tank. This is not a rare occurance. The crack usually goes through the water inlet opening or the tank lever hole. It is normally caused by corrosion occurring at those points and creating stress which eventually cracks the tank.

: : The strangest thing happened the other day and I was wondering if anyone out there has ever had
: : a similar experience.

: : I was standing near the bathroom and heard a loud snap, the toilet reservoir had split open in two
: : separate cracks at one end of the tank.

: : The toilet was about 25 years old and didn't have any previous visible cracks.

: : Fortunately I was home at the time and was able to shut off the water supply immediately, can
: : only imagine the mess had I been out at the time.

: : Anyone out there have a take on this ? (as to what may have caused this)

: : Thanks for any help at all.