~[ONOSULFIDES, ETc.--Of the few crystals for which structures have been determined only zinc blende, ZnS, and alabandite, MnS, have received satisfactory treatment. The others to which assignments of structure have been made are wurtzite (ZnS), greenockite (CdS), galena (PbS) and strontium selenide.
Alabandite, MnS.--From spectrographic and powder photographic data and the results of the theory of space-groups it has been shown s4 that alabandite either has precisely the " sodium chloride arrangement " (Fig. 6) or one very close to this grouping. The possibility of such a slight variation from the sodium chloride structure must be considered because there is some crystallographic evidence for less than holohedral symmetry. The probability of such a shift in atomic positions being real does not, though, seem very great. The length of the side of the unit cube (Fig. 6) is determined as: a = 5.214A.U.
Zinc Blende, ZnS.--Zinc blende is one of the first crystals to have been studied with X-rays, and its structure has been investigated with both spectrometric and Laue photographic data.S,~, s6, ,o0, 92 The atomic arrangement which is deduced from these studies gives the atoms within a unit cube 5.42A.U. on a ~ide the co6rdinate positions (Fig.