Original paper

Al3Si2O7(OH)3, phase Pi (formerly piezotite): Crystal structure of a synthetic high-pressure silicate rediscovered

Daniels, Peter; Wunder, Bernd

European Journal of Mineralogy Volume 8 Number 6 (1997), p. 1283 - 1292

19 references

published: Jan 8, 1997
manuscript accepted: Jul 18, 1996
manuscript received: Aug 11, 1995

DOI: 10.1127/ejm/8/6/1283

BibTeX file

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Abstract

Abstract The crystal structure of the triclinic high-pressure phase with the chemical composition Al3Si2O7(OH)3 (a = 6.0885(6) Å, b = 7.2832(9) Å, c = 7.7234(9) Å, α = 115.71(1)°, ß = 88.85(1)°, γ = 92.89(1)°; space group P1, Z = 2), here named phase P1, is based on a cubic closest packing of oxygen atoms. The characteristic pattern of occupied polyhedra produces layers of interconnected AlO6-octahedra and single SiO4-tetrahedra. The most probable location of hydrogen atoms, not found in the X-ray single-crystal analysis, is derived from calculated bond valence sums. Comparison with other structures in the system Al2O3-SiO2-H2O relates phase Pi to phyllosilicates and other neso-subsilicates with similar chemical composition. Structural comparisons also show that, in this system, there are trends in the development of polyhedral topologies and oxygen packing with increasing pressure.

Keywords

phase Pipiezotitecrystal structurecrystal chemistry