A Prince Rupert's drop, made by dripping molten glass into water, has a head so strongly compressed you can strike it with a hammer, yet snipping its thin tail makes the whole thing vanish into powder as a crack races through it at roughly 1,450 to 1,900 meters per second.

The rapid quench locks the surface in compression and the interior in tension, the same residual stress trick used to make modern tempered safety glass.

Source: The explosive disintegration of Prince Rupert's drops, Philosophical Magazine B