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 e2 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 ∼An₆₆ is provided accordingly.

中文翻译：

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重新研究高温的富含Ca的斜长石长石的I {\ overline {\ bf 1}}结构-单晶中子和X射线衍射研究。

使用单晶中子和X射线衍射分析了在高温下形成的四个天然富含Ca的斜长石长石的结构。ORNL散裂中子源（美国田纳西州）上的中子飞行时间劳厄衍射仪与单晶X射线衍射仪相结合，能够揭示有关这些已经深入研究的结构的一些新细节。从中子衍射数据中提炼出的分裂氧原子显示出Ca–Na有序化和沿c轴的各向异性有序化的潜在机理。所研究的样品所覆盖的组成范围对于结构而言非常罕见。无比调制的e某些斜长石样品的2结构很容易与衍射图谱中的结构混淆，这使一些以前发表的结构受到质疑。提出了不富含钙的斜长石长石的不完全相图，以解释该组成范围内结构的稀有性，并相应地提供了组成〜An ₆₆的时间-温度-转变图。