Original paper

Synthesis and structural properties of clinopyroxenes of the hedenbergite CaFe2+Si2O6 - aegirine NaFe3+Si2O6 solid-solution series

Redhammer, Günther J.; Amthauer, Georg; Lottermoser, Werner; Treutmann, Werner

European Journal of Mineralogy Volume 12 Number 1 (2000), p. 105 - 120

22 references

published: Feb 7, 2000
manuscript accepted: Sep 15, 1999
manuscript received: Apr 6, 1999

DOI: 10.1127/0935-1221/2000/0012-0105

BibTeX file

ArtNo. ESP147051201025, Price: 29.00 €

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Abstract

Abstract Clinopyroxenes along the solid solution hedenbergite-aegirine M2[Ca2+1-xNa+ x]M1{Fe2+1-xFe3+ x}Si2O6 were synthesized using hydrothermal techniques at 4 kbar. Different temperatures and redox conditions were used to determine optimum synthesis conditions and the stability range of individual compositions in the T - log fO2 field. Synthesized samples were characterized using microprobe analysis, X-ray powder diffraction and Mössbauer spectroscopy at 298 K and 80 K. The structure was refined in the C2/c space group by means of the Rietveld method. Along the solid-solution series between hedenbergite (ao = 9.8448(6) Å, bo = 9.0296(6) Å, co = 5.2452(4) Å, β = 104.813°) and aegirine endmembers (ao = 9.6547(6) Å, bo = 8.7941(8) Å, co = 5.2944(4) Å, β = 107.398°), the changes in unit cell dimensions show significant deviations from linearity. Mean and individual M1-O distances decrease linearly from hedenbergite to aegirine; mean M2-O and T-O distances do not change significantly, whereas individual length may vary. While in hedenbergite the coordination of the M2 site is 6+2, it is 4+4 in aegirine. The Mössbauer spectra of the solid-solution endmembers display narrowly split resonance absorption lines with hyperfine parameters typical for Fe2+ (δ = 1.18 mm/s, Δ = 2.25 mm/s at 298 K) and Fe3+ (δ = 0.38 mm/s, Δ = 0.30 mm/s at 298 K). Fe occupies only the M1 site. The Fe2+ resonance absorption is somewhat broadened in the 80 K spectra of the solid solution, which is due to a distribution of quadrupole splittings.

Keywords

hedenbergiteaegirineRietveld refinementMössbauer spectroscopy