I was once sat in a doctor's waiting area that had an array of tempered glass walls. There were about a dozen other people in the waiting room with me.

All of a sudden something like a gunshot went off and one of the glass panels exploded. Everyone shit themselves. No-one was anywhere near this panel. No gun toting loonies in sight. It just sort of decided to explode.

Nickel sulphide phase changing most likely.