I was in the caverns today when I came across a nubbin of metal that had been left by someone. I like to clear nubbins so rocks can regenerate so I struck it with my Fancy Pick and nothing happened. I struck a second time and got the message, "This is not the rock you seek." Lol! I thought that maybe it works like gardens and was waiting for the original miner to return. So I waited a while and tried a third time - "This is not the rock you seek." OK, I went to the next street and immediately returned and there was no nubbin there. Perhaps I just could not see it?