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On the crystal chemistry of londonite [(Cs,K,Rb)Al4Be5B11O28]: A single-crystal neutron diffraction study at 300 and 20 K
-
G. Diego Gatta
,
Pietro Vignola
Veröffentlicht/Copyright:
2. April 2015
Abstract
The crystal chemistry of londonite, a rare Cs-bearing mineral [ideal chemical formula: (Cs,K) Al4Be4(B,Be)12O28; a = 7.3098(2) Å at 300 K, space group P4̅3m] from the granitic pegmatites of the Antsongombato Gem Mine, Betafo district, Madagascar, has been reinvestigated by means of wavelength dispersive X-ray spectroscopy, laser ablation-inductively coupled plasma-mass spectroscopy, inductively coupled plasma-atomic emission spectroscopy, X-ray powder diffraction, and single-crystal neutron diffraction at 300 and 20 K. Single-crystal anisotropic structural refinement at 300 K gave a final agreement index R1 = 0.0479 for 32 refined parameters and 416 unique reflections with Fo > 4σ(Fo). The analysis of the difference-Fourier maps of the nuclear density discounts the presence of hydroxyl groups, as wrongly reported in some of the previous studies. The structural refinements and the chemical analyses suggested that: the tetrahedral 4e site (at x ~ 0.258) is mainly occupied by Be, but a low amount of B (~3%) likely occurs; the tetrahedral 12h site (at x ~ 0.248) is mainly occupied by B, but a significant fraction of Be (~12%) is present; the octahedral 4e site (at x ~ 0.361) is fully occupied by Al; and the 1a site (at x = 0, with CN = 12) is mainly occupied by Cs, with Rb and K. The significantly high amount of B2O3 (~50 wt%) and Cs+Rb(CsO2+RbO2 ≥ 8 wt%) makes the synthetic counterpart of londonite of interest as a potential neutron absorber or a potential host for nuclear waste.
Keywords: Londonite; crystal chemistry; crystal structure; single-crystal neutron diffraction; low temperature
Received: 2010-3-16
Accepted: 2010-6-3
Published Online: 2015-4-2
Published in Print: 2010-10-1
© 2015 by Walter de Gruyter Berlin/Boston
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Schlagwörter für diesen Artikel
Londonite;
crystal chemistry;
crystal structure;
single-crystal neutron diffraction;
low temperature
Artikel in diesem Heft
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- A new method for quantitative petrography based on image processing of chemical element maps: Part I. Mineral mapping applied to compacted bentonites
- A new method for quantitative petrography based on image processing of chemical element maps: Part II. Semi-quantitative porosity maps superimposed on mineral maps
- Enhancement of solid-state reaction rates by non-hydrostatic stress effects on polycrystalline diffusion kinetics
- (H3O)Fe(SO4)2 formed by dehydrating rhomboclase and its potential existence on Mars
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- Kinetics of Fe-oxidation/deprotonation process in Fe-rich phlogopite under isothermal conditions
- On the crystal chemistry of londonite [(Cs,K,Rb)Al4Be5B11O28]: A single-crystal neutron diffraction study at 300 and 20 K
- High-pressure melting of wüstite
- Primary Nb-Ta minerals in the Szklary pegmatite, Poland: New insights into controls of crystal chemistry and crystallization sequences
- Evolution of the interlayer space of hydrated montmorillonite as a function of temperature
- Morphology of pyrite in particulate matter from shallow submarine hydrothermal vents
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- Crystal chemistry and origin of grandidierite, ominelite, boralsilite, and werdingite from the Bory Granulite Massif, Czech Republic
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: III. Thorneite, Pb6(Te26+O10)(CO3)Cl2(H2O), the first mineral with edge-sharing octahedral tellurate dimers
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: IV. Markcooperite, Pb(UO2)Te6+O6, the first natural uranyl tellurate
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: V. Timroseite, Pb2Cu52+(Te6+O6)2(OH)2, and paratimroseite, Pb2Cu42+(Te6+O6)2(H2O)2, two new tellurates with Te-Cu polyhedral sheets
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- The determination of sulfate and sulfide species in hydrous silicate glasses using Raman spectroscopy
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