Al₂SiO₅, Al₂GeO₅ and Cr₂GeO₅ kyanites: X-ray powder data and infrared absorption spectra

Kyanite phases Al₂SiO₅ (I), Al₂GeO₅ (II) and Cr₂GeO₅ (III) were synthesized at 20 kb/1000°C (I, II) and at 1 atm/1150°C (III). Powder X-ray patterns for II and III are presented in comparison with that of I. Triclinic lattice constants are a₀ = 7.127 (7.253, 7.422), b₀ = 7.858 (8.011, 8.244), c₀ = 5.570 (5.649, 5.815) Å, α = 89.99 (89.97, 90.58), β = 101.22 (101.23, 101.10), γ = 106.04 (106.05, 106.01)°, and V₀ = 293.6 (308.9, 339.9) ų for the kyanite phases I (II, III, respectively). Infrared absorption spectra of I (II, III) were measured between 1400 and 200 cm⁻¹. Band shifts produced by the isomorphous substitutions allow tentative band assignments of the Al₂SiO₅-kyanite spectrum: 1032, 1009, 940 cm⁻¹ ν₃ (SiO₄); 898 cm⁻¹ ν₁ (SiO₄); 720, 438 cm⁻¹ ν₄, ν₂ (SiO₄) ?; banes between 674 and 505 cm⁻¹ and at 467 cm⁻¹ are mainly due to octahedral Al–O vibrations.