Abstract
HAlSi4O10 was prepared from natural petalite (castor), LiAlSi4O10, by Li/H exchange in H2SO4 (300°C). The crystal structure was determined by X-ray methods from a twinned crystal [a = 5.867(3), b = 4.927(3), c = 7.524(4) Å, α = 93.0(l), β = 113.1(1), γ = 90.1(1)°, space group P1, Z = l, R = 0.053 for 1011 reflections and 133 variables]. The topology of the Si4O10 layers of petalite is not affected by ion exchange. The Al atoms are rearranged, however: Half of the Al atoms are on positions corresponding with those in petalite, the other Al atoms are on former Li positions. The remaining tetrahedral positions are empty. As a consequence the a translation in HAlSi4O10 is only half as long as in petalite. The SiO4 and AlO4 tetrahedra are rotated during site exchange: one of the former O – O edges in AlO4 resp. LiO4 tetrahedra (now a vacant tetrahedral site) is shortened to 2.567(2) Å. Neutron powder patterns were recorded on HAlSi4O10 and DAlSi4O10 at 5 K and 293 K. Rietveld refinement allowed the location of the hydrogen atom in the short O … O contact.
