Crystal-structure refinement of hydrogen-rich staurolite

The crystal structures of two samples of hydrogen-rich staurolite have been refined to R indices of ~2% using single-crystal MoK? X-ray data. There is considerable occupancy of the M(4A) and M(4B) sites. The sums of the cations for each structure are 29.48 and 29.31 apfu, respectively, in agreement with the high H contents of the crystals. The total occupancy of the M(3) sites is variable; the vacancy content of M(3) correlates linearly with the hydrogen content of the crystal, confirming previously suggested mechanisms of substitution involving variable occupancy of M(3) in staurolite. -Authors