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Revisiting the I structures of high‐temperature Ca‐rich plagioclase feldspar – a single‐crystal neutron and X‐ray diffraction study
Author(s) -
Jin Shiyun,
Wang Xiaoping,
Xu Huifang
Publication year - 2018
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520618003219
Subject(s) - plagioclase , neutron diffraction , crystallography , diffraction , single crystal , feldspar , diffractometer , materials science , neutron , spallation neutron source , phase diagram , crystal structure , phase (matter) , physics , chemistry , nuclear physics , neutron source , optics , quartz , composite material , quantum mechanics
The structures of four natural Ca‐rich plagioclase feldspars formed at high temperature were analysed using single‐crystal neutron and X‐ray diffraction. The neutron time‐of‐flight Laue diffractometer at the ORNL Spallation Neutron Source (Tennessee, USA) combined with a single‐crystal X‐ray diffraction instrument were able to reveal some new details about these already intensively studied structures. The split oxygen atoms refined from the neutron diffraction data show the underlying mechanism of Ca–Na ordering and the anisotropic ordering along the c ‐axis. The compositional ranges covered by the samples studied are quite rare for structures. The incommensurately modulated e 2 structure of some plagioclase samples can easily be confused with an structure from the diffraction pattern, which puts some previously published structures into question. An incomplete phase diagram for Ca‐rich plagioclase feldspar is proposed to explain the rarity of the structure in this compositional range, and a time–temperature–transformation diagram for the composition ∼An 66 is provided accordingly.