Since diamond gems come from deep within the earth, most of them will have inclusions and surface defects called blemishes. In most cases, inclusions may be crystals of a foreign material or structural imperfections such as tiny fractures. Diamonds with the least inclusions are rarer and the most valuable. By applying the international system of classifying diamonds (mc) created by the GIA, the clarity grade is determined by its overall appearance. Clarity is one of the 4C's in diamond rating, the others being carat, color and cut. Under ten times magnification, a clarity grade is determined by the positioning, the quantity, the size, the color and the nature of impurities.