The Four C’s – carat, clarity, cut and colour determine the value of a single diamond. The rating assigned to each characteristic determines the diamond’s overall value. Diamonds are valuable because the global supply of diamonds is limited. However, because there is so much variability in the four C’s across individual diamonds, or because there is no set unit price for diamonds that is recognized in worldwide markets, the value of diamonds is not very predictable or stable (unlike gold). It is therefore in one’s best interests to buy diamonds that are higher up on the Four C’s grading scale or are very rare because they are large or fancy coloured.