Rocks can be mined at quarries. The player can instruct a villager to be a quarryman which works at quarries and mines rock. Another villager can be a rock hauler, those villagers collects rock and adds it to a stockpile.
Rock can be stored at both a small and large stockpile, just like many other materials and resources.
Rock appears to be 3 grey and dull objects with a few sharp corners.
Kaito White, 13:34, April 19, 2012 (EST)