I have a friend who’s a budding amateur geologist. He loves going on little nature trips every weekend and picking up interesting rocks and stones he sees. He sometimes then turns his little finds into very interesting craft items such as paperweights or bookends. I once asked how he got them so nice and shiny and it turns out that he uses rock tumblers to polish his little stones to a fine finish. They make really pretty gifts and he was really nice to give some of them to me as souvenirs.