What unusual property of water is responsible for frost wedging?

1. The fact that water requires more volume when it solidifies (freezes). Most liquids will turn into a solid when they freeze and in the process of freezing, take a smaller volume. But water is unusual in that when it freezes, it increases its volume. And during that expansion, it can exert a LOT of force. If water is in an enclosed space, it can exert about 1000 times atmospheric pressure against its surroundings.

The property of water that it expands and becomes less dense as it freezes. The property is unusual because it is not the case in other liquids.

Ice wedging is a form of mechanical weathering or physical weathering in which cracks in rock or other surfaces fill with water, freeze and expand, causing the cracks to enlarge and eventually break.