What is the difference between a rock and a stone? Had we been proceeding logically, this issue would have come first. Many will say there is no difference. But if we ask a geologist, the answer comes out pat: a stone is a rock that's been put to use: stone hammer, rip-rap, gravel, wall, paving stone, tombstone, milestone, statue. Now, a geopoet, I surmise, will give the same answer, but where the geologist snaps a lid shut, the geopoet opens Pandora's box. What happens between rock and stone is simply everything human, from the modifications necessary to make homes to, at the other extreme, the excesses of ownership and exploitation which submit all ends to ours. So another answer might be: rock is as old as earth is; stone is as old as the superfamily Hominoidae.
What's the difference between rock and stone? In their natural setting, they're rocks; when we bring them into the garden, they're stones. Each has its own individual character.