Ever heard of a Prince Rupert’s drop? Me either. It’s formed by dropping a blob of molten glass into water, causing the outside of the blob to cool much faster than the inside. Result: weird internal pressures that make the drop incredibly strong and impossible to break. But…you can explode it.
Check out the video here, which shows what’s happening in awesome slow motion, and also has a pretty amusing illustration method for the internal stresses. Max resolution and full screen is advised.