Carbon Ownby P D, Yang X, Liu J Journal of the American Ceramic Society 75 (1992) 1876-1883 Calculated X-ray diffraction data for diamond polytypes Note: rhombohedral, 21R structure Note: theoretically calculated structure values _database_code_amcsd 0014071 2.5221 2.5221 43.2450 90 90 120 R-3m atom x y z C1 0 0 .01786 C2 0 0 .17262 C3 0 0 .20833 C4 0 0 .26786 C5 0 0 .30357 C6 0 0 .41071 C7 0 0 .44643