What happens to igneous rocks when they undergo weathering and erosion?
Depending on the type of rock, the erosion will grind the crests of the igneous matter off, to create fine soil and gravel, and the rock itself will become quite smooth. If the erosion is being caused by water, the results can be much faster and the rocks much smoother. Funnily, the offstream of particles from the eroded rocks can settle and compact and become sedimentary rocks, after a while.