Rounds are the most popular shape that diamonds are cut into. It is also the most brilliant of all the cuts. You may have heard of a term called "Ideal Cut". This term refers to the attempt to cut a diamond into the best proportions to achieve maximum brilliance. Rounds are the most expensive cuts, and with good reason. It is usually possible to retain more weight from a Rough (unpolished) Diamond if it is cut into a Fancy shape than if it is cut to a Round.