ABSTRACT

A new aluminium silicate has been produced under hydrous conditions from Al₂O₃-SiO₂ oxide mixes with Si/Al ratios close to unity, at pressures greater than 100 kilobars and at about 1, 000°C. X-ray powder photographs indicated one dominant new phase. From analyses of the electron diffraction Laue zones of minute fragments (∼1μm), a monoclinic structure that fitted the X-ray powder results was identified. This monoclinic structure is described in terms of nine close-packed layers of oxygen with the unit cell containing 72 oxygen atoms. Assuming Si/Al equals 1, the composition of this phase is Al₂₀Si₂₀O₇₂H₄. The calculated density of 4.03 g/cc is in good agreement with the value of 4.02 g/cc estimated from the refractive index measurements.