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Na-feldspar: temperature, pressure and the state of order

Kroll, Herbert; Bambauer, Hans Ulrich; Pentinghaus, Horst

In feldspars, mean tetrahedral T–O bond lengths (T = Al,Si) are the standard measure of the tetrahedral Al content. However, for a sophisticated assessment of the Al,Si distribution, factors have to be accounted for (1) that cause individual T–O bond lengths to deviate from their tetrahedral means and (2) that cause mean tetrahedral lengths to deviate from values specified by the Al content. We investigated low albite, Na[AlSi3O8], from six X-ray crystal structure refinements available in the literature. The Al,Si distribution of low albite is fully ordered so that Al,Si–O bond length variations result only from bond perturbing factors. For the intra-tetrahedral variation ΔT–O≡T–O−⟨T–O⟩, only two factors turned out to be effective: (1) the sum of bond critical point electron densities in the Na–O and T–O bonds neighbouring the T–O bond under consideration and (2) the fractional s-bond character of the bridging oxygen atom. This model resulted in a root mean square (rms) value for ΔT–O of only 0.002 Å, comparable to the estimated standard deviations (esd's) routinely quoted in X-ray and neutron structure refinements. In the second step, the inter-tetrahedral differences Δ⟨T–O⟩≡⟨T–O⟩−⟨⟨T–O⟩⟩ were considered. ... mehr

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Verlagsausgabe §
DOI: 10.5445/IR/1000130098
Veröffentlicht am 26.02.2021
Cover der Publikation
Zugehörige Institution(en) am KIT Fakultät für Bauingenieur-, Geo- und Umweltwissenschaften (BGU)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2020
Sprache Englisch
Identifikator ISSN: 1617-4011
KITopen-ID: 1000130098
Erschienen in European journal of mineralogy
Verlag Copernicus Publications
Band 32
Heft 4
Seiten 427–441
Vorab online veröffentlicht am 30.07.2020
Nachgewiesen in Scopus
Web of Science
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