I found a good sized rock, maybe milky quartz or something similar, on Mt. Washington, and carried it down with me. For some reason, I wanted a souvenir of the climb, and this fit the bill. I’m not sure I realized, at the time, that it was probably frowned upon, or maybe illegal, to remove pieces of the mountain, but it was such a cool-looking specimen and I figured no one would miss it.
There’s probably something else, but it’s not coming to mind at the moment.