Inhomogeneous mosaicity in extinction correction

Extinction effects in ground spherical samples can differ between the surface and the interior. The formula: |F_inhom| = |F_calc|[1 + x(d² −1)]^1/2/d, with d = (1 + 2gβ|F_calc|²)^1/4, where x is the non-extinct volume fraction of the crystal, g a parameter describing the mosaic and βa geometrical expression calculable at data reduction time, has been applied in the least-squares refinement of two low-quartz samples and one corundum sample. The effect is considerable for one quartz sample where the mosaic block size is 5.2 μm, small for the other quartz sample where the mosaic block size is 1.4 μm and unimportant in corundum where the block size is 0.4 μm and where extinction is larger than in the previous sample. This observation is compatible with the expectancy that the effect should essentially depend on the mosaic block size.