The mile per second speed of the fracture is mind blowing. But... now... think about the speed of det-cord like they use to "slice" concrete columns in old buildings, that stuff burns at a rate of FOUR miles a second!!

Glass is weird stuff to say the least. It's not even an actual solid, supposedly. It flows so slow that windows will thicken at the bottom over hundreds of years. It has no organized crystal structure like most metals. That's why it gets plastic when it heats up; there's no melting point. Metals just suddenly turn to liquid at some point, but not glass.