"Well, jewelry is one, or just for display, or studying the animals that lived in them. You can carve them into tools, and when there's enough of them and enough time passes they turn into stone that's great for building stuff." Oops, fossils got in there anyway. "And there's one kind that can be used as an instrument!" That might be more Armin's speed. "We might even be able to find one if we really looked. This beach seems kind of tropical."