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

Abstract

The potential of synchrotron radiation Lane diffraction pattems for structure determination and for identification of small single crystallites is illustrated. Diffraction pattems were recorded for several crystallites, _<20 l.tm 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,

Recording Diffraction Data for Structure Determination for Very Small Crystals

“…(6) Cu2(OH)2C()3 or (Cu,Zn)2(OH)2(X)3, very poor quality crystal from sample of mineral rosasite, final R = 0.12 for 153 reflections / . 2cr(l) (Kariuki & Harding, 1995).…”

Application of Energy-Resolved Measurements to Laue Diffraction: Determination of Unit-Cell Parameters, Deconvolution of Harmonics and Assignment of Systematic Absences

“…Additionally, this method may be a useful complement to previously described studies of very small crystals (Kariuki & Harding, 1995). The dimensions of the alkali halide crystals used here are in the range of many crystalline minerals.…”

X-Ray synchrotron radiation in physicochemical studies

“…The unprecedented volume for a single crystal of gold studied by this method 118 is *10 73 mm 3 . During recent years, special techniques for data recording and processing have been developed in this field, which allow at present the ab initio (i.e., without any a priori structural models) solution of relatively simple structures solely from Laue diffraction data 119,120 and refinement of structures of any complexities. 121 Yet another direction in the development of synchrotron X-ray crystallography is magnetic scattering.…”

“…A major disadvantage of the conventional MoÈ ssbauer spectroscopy is a limited number of monochromatic g-sources available. The predominant part of all MoÈ ssbauer studies is performed for a few elements which have convenient g-active isotopes, such as 57 Fe, 119 Sn, 121 Sb, 151 Eu. In principle, utilisation of SR eliminates this restriction since X-ray radiation with continuous energy distribution up to 100 keV and higher is made available (this is particularly true for the third-generation SR sources and insertion devices).…”