Uncut Diamonds - An uncut diamond is a stone that has not been shaped | Uncut diamonds are also referred to as rough diamonds | A diamond's carat is a measure of weight (1 ct = 200 mg), and in general, bigger stones are more valuable since they are rarer. However, rough diamonds of a higher carat are not always more expensive than smaller ones. ... All else being equal, bigger diamonds cost more per carat than smaller ones when cut.