Test the hanging loop. I bet it is 18K. A lot of crooks are using the clasp loop to mark a piece of junk jewelry. There is a lot of dishonest practices going on with some people in the precious metals market. I had the occasion to deal with one recently. My wife took a couple of fines to this jeweler to have sized. When we got the items back they had been severely shaved and they appeared to have been done with a dremel tool. When my wife approached the person he admitted he had used a dremel tool to shape the rings after he sized them. She said he was working on some pieces while she was talking to him and he had quit a pile of gold shavings where he had shaved another persons piece. I wanted to go ballistic on him but she wouldn't allow it. He even went so far as removing the karat stamp on a couple of rings that there was absolutely no reason for him to have to have done. Word of advice take pictures and weigh items before taking to anyone to have jewelry worked on.