http://www.cnr.it/ontology/cnr/individuo/prodotto/ID174753
Determination of site population in olivine: warnings on X-ray data treatment and refinement (Articolo in rivista)
- Type
- Label
- Determination of site population in olivine: warnings on X-ray data treatment and refinement (Articolo in rivista) (literal)
- Anno
- 2000-01-01T00:00:00+01:00 (literal)
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- MERLI M.; OBERTI R.; CAUCIA F.; UNGARETTI L. (literal)
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- Note
- ISI Web of Science (WOS) (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
- CNR-Centro di Studio per la Cristallochimica e la Cristallografia (CSCC), via Ferrata 1, I-27100 Pavia, Italy;
Dipartimento di Scienze della Terra, via Ferrata 1, I-27100 Pavia, Italy (literal)
- Titolo
- Determination of site population in olivine: warnings on X-ray data treatment and refinement (literal)
- Abstract
- Leverage analysis enables identification of reflections with the greatest influence on the estimate
of each refined variable, and thus may be an important tool to improve standard structure-refinement
procedures, especially in the case of minerals with complex composition. In this work, leverage
analysis was used to investigate in detail the influence of each reflection in high-resolution X-ray
diffraction data collected from olivine, a mineral often used to model order-disorder processes and
to calculate temperatures of closure and cooling rates of host rocks. Particular attention was paid to
the estimate of the scattering power at the cation sites, that are crucial for the above studies. Various
procedures for data correction and refinement were also investigated, and the different possible
choices were compared to choose the strategy that provides the best results.
The presence of high-leverage weak reflections in olivine strongly suggests that systematic data
truncation according to intensity threshold should be avoided. The estimates of the site-scatterings
obtained under the different conditions tested are very close (always .3 ?Ð); they are often smaller
than those which may be obtained from electron-microprobe analysis under different experimental
conditions or on inhomogeneous (zoned) crystals. Chemical data should thus not be routinely used
to constrain the refinement procedure and/or to optimize final site-populations, provided that appropriate
errors are given; on the other hand, they are valuable to appreciate the presence and the amounts
of very minor, sometimes unexpected, substituents. Our tests show that precision better than 0.001
in site-occupancy determination (sometimes claimed in the literature) is probably not achieved. (literal)
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