I suggest taking it to various local jewelers in your area. Most buy pieces, even if they don't advertise that they are buying. They usually have better prices than the national gold places or the places that set up in hotels and such. Scrap gold prices are pretty good right now. If you have any other gold pieces you're thinking of getting rid of, put them all together. They should be able to give you a price on the spot and then just choose the highest paying place. Diamonds can be tricky. Unless it's a very high quality, large solitaire stone, you won't get much for it, unfortunately.