The compounds Ag 7 AsS 6 and Ag 7 SbS 6 are apparently stoichiometric in the presence of their respective constituent elements, and require high sulfur fugacity for stability. X-ray diffraction analysis of compositions intermediate between the two indicate a continuous solid solution series. Up to 12.5 weight percent Cu can substitute for Ag in the arsenic compound at 340 degrees C, and 3.5 percent Cr in the antimony compound. The unit cell edges are 10.48A and 10.60A, respectively, for X-ray data indexed on the basis of a primitive isometric unit cell. Two localities in Colorado may provide natural occurrences.

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