This Rocks! adds little rocks, sticks, pinecones, seashells, starfish, and geysers to your minecraft world to make it feel more natural.
You can break a rock to get splitters that you can craft into their respective blocks, except for the gravel rock, which drops flint.
The sticks drop normal minecraft sticks, the pinecones drop spruce saplings, the seashells rarely drop Nautilus Shells, and the starfish drop the starfish block for decorating.
The geysers get activated once you get close to them, the overworld geysers will just boost you up, but the nether geysers will burn you!
You can cycle through the different states of the blocks in creative mode.
For an even better experience, I recommend using this mod alongside Wild World, which also adds many nice decorative worldgen features.