Minecraft wiki entry for Caves_%26_Cliffs, associated text: An opaque block that appears grassy on all sides.
Using bone meal can cause it to grow grass, tall grass, moss carpets and both types of azalea bushes on it and in its vicinity.
Bone meal can also cause it to grow over (expand) and convert stone surfaces, sand, dirt, etc. but not grass surfaces.
Breaks when pushed by a piston.