It's mine, I left it there. Please return it, I have not slept in ummm months.
Seriously, keep it and enjoy it. No matter its' value it just isn't that big of a deal. I am sure its' owner misses it but you found it in YOUR home. It would take too long to locate the owner and it isn't that important. If you feel really bad I just saw a really compelling episode of Oprah about the way middle eastern women are treated. It would cost 25 bucks a month to help them. Sell the ring on ebay and donate the money to this worthy cause.
www.oprah.com