High-resolution synchrotron-radiation powder data for quartz and MgzGeO4, an olivine homologue, were obtained with a 365 mm long parallel-slit collimator with 0-05 ° aperture. The crystal structures were refined using a pseudo-Voigt profile fitting function and POWLS. Fourier maps were calculated from the measured structure factors of the germanate. The results for quartz were in good agreement with singlecrystal data and R(Bragg) increased from 1.35 to 2-20% as the number of reflections included in the refinement increased from 46 to 119; the e.s.d.'s of the positional parameters were 4 to 8 x 10 -4. The germanate gave R(Bragg) 4.85% using 77 Miller planes and the e.s.d.'s were 4 to 42 x 10 -4. Special attention was given to the profile fitting function and the nonrandom particle distributions. The JCPDS Diffraction File Nos. will bc reported in a later communication.

X-ray powder diffractometry with storage-ring radiation was used to test various aspects of a method for refining simple crystal structures (Si, CeO2 and Co304). Excellent powder patterns were obtained with 0.17 ° resolution parallel slits and IA X-rays. The intensities were determined with a double-Gaussian profile-fitting function and used in the powder leastsquares refinement program POWLS. Except for Si, the peaks were broadened because of small particle sizes. The R(Bragg) values were in the range 0-4-1.7%.

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The use of synchrotron powder diffraction patterns to determine anomalous scattering contributions is described. The method is illustrated by the determination off' of Yb at the Yb LIII absorption edge. Four data sets were collected with four wavelengths, fitted with Gaussian profiles and the integrated intensities used to determine by least-squares methods the crystal-structure parameters and the real part f' of the anomalous dispersion. The derived f' values had a precision of +0.2 electron units and averaged 32% higher than the Cromer-Liberman theoretical values.