Micro-sized Samples Research Articles

Étude chimique et structurale d'un sulfure naturel : la zinckénite

Although the structural crystallography of zinckenite has been studied by several authors, the quality of the available analysis of this mineral was not high enough to settle the question of cell content. Largely on the basis of the specific gravity determination, some authors suggested the composition PbSb₂S₃ ; but D. C. Harris (1965) analyzed the mineral by X-ray spectrography, using new methods developed for microsize samples ; results gave atomic ratios for Pb/Sb of 6/14, and Harris conclued : 12 [6PbS-7Sb₂S₃] was the most likely cell content for zinckenite. The present work was carried out to determinate chemical composition from the results of structural analysis. The crystal structure has been studied carefully by classical methods. Further adjustments were obtained by least-square method to a final discrepancy index of R = 0.09. The interpretation of these results (structure in domains, with unidimensional fibers of A₃ symmetry and parameter c' = 8.64 Å) explicates the zinckenite may exist either as a three dimensional ordered phase, or as a disordered phase with stacking faults parallel to [001]. So, this study gives an explanation of polysynthetic twinning, and permits to conclued for zinckenite to the formula : Pb₁₊ₓSb₄₋ₓS₇ with 0.50 ≤ x ≤ < 0.67.