While many diamonds are incredibly beautiful, no two are alike. Most diamonds have flaws, called inclusions, which are unique to each diamond. Inclusions can be crystals, feathers and lines generally not seen unless magnified. Clarity is determined by the absence of inclusions. The fewer the inclusions, the more rare and more valuable the diamond. Clarity grades are determined by the number, size, color and location of inclusions. The smaller and less visible the inclusions, the higher the diamond's grade.