The hydrogen locations and chemical composition of staurolite

Abstract

A two-dimensional neutron-diffraction study of staurolite revealed the hydrogen locations in the c-axis projection. Hydrogen atoms are in the form of OH at the 0(1A) and 0(1B) positions according to the site notation given by Smith (1968), With the aid of nuclear-magnetic-resonance studies, which yield an effect of proton-to-Fe2+ interactions, and based upon Smith's positional parameters of Fe2+, the hydrogen locations in space have been determined. They are in the two sets of four-fold sites: P(1A), x = 0.1218, y = 0, z = 0.072 P(1B), x = 0.1218, y = 0, z = 0.424. For the crystal we used, three protons per cell are statistically distributed over the eight positions. The locations are in the oxygen ootahedra at the Al(3A) and Al(3B) sites, but they are nearly in the octahedral faces defined by O(1) and two O(3) atoms. The position of hydrogen atoms is such that a weak bifurcated hydrogen bond occurs between O(1) and two O(3) atoms.