Citation: Wyckoff, R. W. G. (1935). http://jcrystal.com/steffenweber/gallery/StructureTypes/st4.html & page 64 from the second edition supplement of The Structure of Crystals by Wyckoff R W G. published by Reinhold Publishing Corporation, INC,Camden,N. J. in 1935. The second edition supplement of The Structure of Crystals, , pp. 64-64.