Minecraft wiki entry for Grass_carried, associated text: It can be broken instantly.[2]
It does not drop anything at all when broken.[2]
It does not have an icon in the inventory.[3]
It cannot be turned into farmland.[4]
Blocks which require a dirt-like block below them to exist, such as flowers and sugar cane, cannot be placed on it.[4]
Placing an opaque block on top on it does not gradually convert it to dirt.