THE 4C CRITERIA Diamonds basically have very different characteristics. For example, looking at two diamonds of the same size, one could assume that both are worth the same amount. However, this is not entirely true, because if there are even small differences, the effect of a diamond and its value are completely different. The best-known criteria for classifying a diamond in terms of quality and value are the so-called four Cs: Carat, Clarity, Color and Cut. Carat Color Clarity (purity) Cut