The real topological conÞ guration of the extra-framework content in alkali-poor beryl: A multi-methodological study
-
G. Diego Gatta
,
F. Nestola
Abstract
The crystal structure of alkali/water-poor beryl (H2O + Na2O + Cs2O < 1.2 wt%) was reinvestigated by means of laser ablation inductively coupled plasma mass spectroscopy, thermogravimetric analysis, neutron diffraction, and polarized infrared spectroscopy to determine the real topological configuration of the extra-framework content in the six-membered ring channels. Analysis of the nuclear density Fourier map suggests that the (water) oxygen is located along the sixfold axis at the 2a site (0,0,1/4), whereas the (water) protons are at -0.028(7), -0.071(3), 0.332(1). The hydrogen atoms are distributed in 6 × 2 equivalent positions, above and below the oxygen site. Geometrical configuration of the water molecule is well defined: the O-H bond distance is 0.949(18) Å and the H-O-H bond angle is 106.9(2.2)°. The H···H vector is oriented at -4° from [001]. This configuration is completely different from that found in alkali-rich beryl, where the H···H vector is perpendicular to [001]. Na is probably located, with the H2O oxygen, at the 2a site. According to the chemical analysis, which shows that the amounts of other alkali and earth-alkali cations are negligible (Rb, K, Mg, Mn ≤ 110 ppm, Ca ≤ 225 ppm, Cs ≤ 430 ppm), no effect of other cations on the extra-framework population was observed in the structural refinement. The final agreement index (R1) of the structural refinement was 0.037 for 34 refined parameters and 160 unique reflections with Fo > 4σ(Fo). The topological configuration of the H2O molecule into the channel is confirmed by the spectroscopic investigation. Polarized single-crystal IR spectra show that the H2O molecule is oriented with the molecular symmetry axis perpendicular to the hexagonal axis and H···H vector parallel (or quasi-parallel) to [001].
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Dana Lecture. Rates of Fe, Mg, Mn, and Ca diffusion in garnet
- An FTIR study of hydrogen in anorthoclase and associated melt inclusions
- First occurrence of iodine in natural sulfosalts: The case of mutnovskite, Pb2AsS3(I,Cl,Br), a new mineral from the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation
- The real topological conÞ guration of the extra-framework content in alkali-poor beryl: A multi-methodological study
- A low-temperature heat-capacity study of synthetic anhydrous Mg-cordierite (Mg2Al4Si5O18)
- Dissolution kinetics of pyrochlore ceramics for the disposition of plutonium
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- Anomalously high Fe contents in rehomogenized olivine-hosted melt inclusions from oxidized magmas
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- Phase transitions and volumetric properties of cryolite, Na3AlF6: Differential thermal analysis to 100 MPa
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- Unique W-rich alloy of Os and Ir and associated Fe-rich alloy of Os, Ru, and Ir from California
- Schreyerite, V2Ti3O9: New occurrence and crystal structure
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