Limestone

Limestone. These are rock formations that spawn on the surface. They are brighter than normal stone, and act as copper. But instead they slowly have moss grow on them. It takes 32-56 days to go 1 stage ahead. You can use shears to take the moss off them, and bonemeal to put it a stage forward. You can also keep it in a stage forever by putting the limestone in the middle and surrounding it with 4 honeycomb.