Calculated X-ray power diffraction patterns for synthetic piemontite on the join Ca2Al3Si3O12(OH)-Ca2Mn〔3+〕3Si3O12(OH)

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X-ray powder diffraction patterns of Ca_2Al_3Si_3O_<12>（OH）-Ca_2Mn^<3＋>_3Si_3O_<12>（OH）series synthetic piemontites were simulated with the Rietan-2000 program to clarify the X-ray powder diffraction pattern of piemontite，using cell parameters，site occupancies and atomic positions refined by the X-ray RIETVELD method．The compositions of Ca_2Al_<3-p>Mn^<3+>_pSi_3O_<12>（OH）-piemontites used were p=0.5，0.75，1.0 and 1.25．The d-values of the strongest line in the simulated powder patterns show a nonlinear variation comparable to nonlinear changes in unit-cell parameters．The calculated powder patterns are very useful for indexing the Miller indices to each reflection in X-ray powder diffraction patterns of natural piemontite，to avoid misindexing and miscalculation of the unit-cell parameters．By comparison with these simulated X-ray powder patterns，we can evaluate the effects of preferred orientation in measured X-ray powder diffraction patterns，which is important for X-ray powder crystal structure analysis．