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Open AccessArticle

Nano-Phase KNa(Si6Al2)O16 in Adularia: A New Member in the Alkali Feldspar Series with Ordered K–Na Distribution

Department of Geoscience, University of Wisconsin—Madison, Madison, WI 53706, USA
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Minerals 2019, 9(11), 649; https://doi.org/10.3390/min9110649
Received: 11 October 2019 / Accepted: 22 October 2019 / Published: 23 October 2019
Alkali feldspars with diffuse reflections that violate C-centering symmetry were reported in Na-bearing adularia, orthoclase and microcline. TEM results indicate elongated nano-precipitates with intermediate composition of KNa(Si6Al2)O16 cause the diffuse reflections. Density functional theory (DFT) calculation indicates ordered distribution of K and Na atoms in the nano-phase with Pa symmetry. K and Na atoms are slightly off special positions for K atoms in the orthoclase structure. Formation of the intermediate nano-phase may lower the interface energy between the nano-phase and the host orthoclase. Previously reported P21/a symmetry was resulted from an artifact of overlapped diffraction spots from the nano-precipitates (Pa) and host orthoclase (C2/m). Adularia, orthoclase and microcline with the Pa nano-precipitates indicate very slow cooling of their host rocks at low temperature. View Full-Text
Keywords: adularia; orthoclase; microcline; primitive alkali feldspar; non-centric symmetry; XRD; TEM; G.P. zone; Na–K ordering adularia; orthoclase; microcline; primitive alkali feldspar; non-centric symmetry; XRD; TEM; G.P. zone; Na–K ordering
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MDPI and ACS Style

Xu, H.; Jin, S.; Lee, S.; Hobbs, F.W.C. Nano-Phase KNa(Si6Al2)O16 in Adularia: A New Member in the Alkali Feldspar Series with Ordered K–Na Distribution. Minerals 2019, 9, 649.

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