Original paper

Oxygen disorder and the hydrogen position in garnet-hydrogarnet solid solutions

Armbruster, Thomas; Lager, George A.

European Journal of Mineralogy Volume 1 Number 3 (1989), p. 363 - 370

17 references

published: Jul 27, 1989
manuscript accepted: Feb 13, 1989
manuscript received: Sep 2, 1988

DOI: 10.1127/ejm/1/3/0363

BibTeX file

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Abstract Difference displacement parameters [ΔU = U(Ö) - U(Si)] evaluated along the tetrahedral d-O vector reveal useful information about the positional disorder of oxygen in garnet-hydrogarnet solid solutions. Observed A {/values, which vary systematically with OH content, are in fair agreement with values predicted from a simple harmonic model. The largest ΔU value is observed for "plazolite" in which two oxygen positions, related by a small displacement along the d-O vector, are about equally populated. Re-examination of the "plazolite" and katoite structures, using structure factors from published studies, confirms that the positional disorder can be described in terms of two oxygen sites (split-atom model) that correspond in position to the sites in "anhydrous" grossular and Si-free katoite. Within the resolution of X-ray diffraction experiments, no relationship can be found between the H position and OH content in the hydrogrossular series.


hydrogarnethibschitekatoitepositional disorderX-ray diffraction