It is loosely defined from my perspective, but I am curious about harder rocks, like granite. Your standard everyday rock tends to be much more brittle and may not have a high metal content. (It will likely have iron in one form or another though.)
Most metals and rocks are crystals in their “normal” state, so I see what you are getting at.
Your username is basically the notation for a crystal oscillator, so it’s gotta count. (Damn the rules!) Quartz is a rock that bends for a commercial purpose, so thats a really good answer, actually.