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