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- Title
Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase.
- Authors
Fredrickson, Rie T.; Fredrickson, Daniel C.
- Abstract
Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P̄1 and P1 (treated in its C̄1 and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1)D superspace, employing both the centro- and noncentrosymmetric superspace groups X̄1(αβγ)0 and X1(αβγ)0, where X refers to a special (3 + 1)D lattice centering with centering vectors (0 0 ½ ½), (½ ½ 0 ½), and (½ ½ ½ 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al)O4 tetrahedra.
- Subjects
ALUMINUM silicates; CRYSTAL structure; PLAGIOCLASE
- Publication
Acta Crystallographica Section B: Structural Science, Crystal Engineering & Materials, 2016, Vol 72, Issue 5, p787
- ISSN
2052-5192
- Publication type
Article
- DOI
10.1107/S2052520616010350