The prices of the diamonds depend largely on the 3 Cs. These 3 Cs are Clarity, Color and Cut. The clarity of the diamond refers to the extent of blemishes or impurities present in the diamonds. Diamonds containing the least of the impurities are considered to be pure and are extremely rare in nature. Adding of blemishes would significantly lower down the price of the diamonds.
Pure diamonds are colorless and therefore priced high. Diamonds that contain colors are considered to contain impurities and that is why they are priced lower than the colorless diamonds. However, if a diamond has high color saturation then it might be priced higher than even the colorless diamonds. The last of the parameters is the cut of the diamond. Diamonds are cut in a way to increase the brilliance and the sparkling nature of the diamonds. More cuts mean that once light enters a diamond it would get refracted more thus resulting in an increased brilliance and subsequent high pricing.