Application of Synchrotron Radiation Laue Diffraction to Small Single Crystals of a Mineral – Structure Determination and Identification

The potential of synchrotron radiation Lane diffraction Patterns for structure determination and for identification of small single crystallites is illustrated. Diffraction Patterns were recorded for several crystallites, ≤20 μm in all dimensions, with the intention of determining an unknown mineral structure. They were the largest particles in the sample. They appeared to represent at least two different phases, but eventually it became clear that neither corresponded to the unknown phase. However, it has been possible to show that both identification and structure determination are practicable from Laue diffraction patterns of crystallites of this size. For one crystallite the diffraction patterns were used to derive unit-cell dimensions and from these the crystallite could be identified as either PbCO₃, cerussite, or SrCO₃, strontianite. Using intensity measurements it could be shown to be PbCO₃. Identification could be similarly achieved for many other small single crystallites, and the procedure is described. For another crystallite, a complete structure determination was carded out and it was then recognized as malachite, Cu₂(OH)₂CO₃. The structure found is in very good agreement with that previously determined by Zigan, Joswig, Schuster & Mason [Z. Kristallogr. (1977), 145, 412–416].