Red Diamonds Red Diamonds are so rare and so expensive that there is hardly ever any talk of them; they are simply unavailable. More than a million dollars per carat, only about 20 stones have been certified as red. Crystal lattice defects showing stress lamination during the formation of the diamond is the main cause of the red color. Modifiers or secondary hues include pink, purple, brown, orange, gray, etc. Enhanced and natural red diamonds can be easily separated because of blackish overtones, lack of graining, and the distinctive absorption patterns of natural red diamonds. Even enhanced red diamonds are considered rare because the color is so hard to achieve. Labs use irradiation and controlled heating to attempt to get the color.