Damn. As a mere human being, I'd surely take it, as you know I have a crystal collection. But as a witch, I think I'd have two different approaches to this situation: I'd either give it back to the sea or simply admire it, because it's perfectly healthy to remember that you can find beauty in something without needing to possess it, or I'd think it was calling me, that it was meant to find its way into my hands. Sometimes nature really does give us little gifts, like an old friend! So, either way, I guess my intuition would give me the answer beforehand.