Redstone blocks can easily be changed into any other block in the game.

To re-create:
1. Wire a 1-redstone-tick clock up to a sticky piston.
2. Place any block on the sticky face of the piston.
3. Turn the clock on.
4. Place a redstone block on the sticky face of the piston as it runs.

The redstone block turns into the same block type as the block behind it when it is pushed by the sticky piston.