I just found a cool video from the Corning Museum of Glass that demonstrates the unusual properties of a glass formation known as the Prince Rupert's Drop. When molten glass is dropped into water to cool, it forms a tear-drop like shape. The outer layer is under high compression, while the inner core is in a state of great tension. The result is a piece of glass that is incredibly strong at the bulbous end, to the point that it can survive hammer strikes. But if you break the thin end, the entire structure explodes into billions of tiny dust-like fragments.
The first video explains what is going on, but doesn't demonstrate the explosion very well.