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Coordination of boron in nominally boron-free rock forming silicates: Evidence for incorporation of BO3 groups in clinopyroxene

Halenius, Ulf; Skogby, Henrik; Eden, Mattias; Nazzareni, Sabrina; Kristiansson, Per LU and Resmark, Jeppa (2010) In Geochimica et Cosmochimica Acta 74(19). p.5672-5679
Abstract
To explore mechanisms of B-incorporation in common chain silicates we have investigated synthetic diopside samples produced under boron-saturated conditions by B-11 and Si-29 magic-angle spinning (MAS) NMR and single-crystal NRA, FTIR, EMP and XRD/SREF techniques. Our samples contain 0.14-0.65 wt.% B2O3. NMR reveals that B is predominantly present in trigonal coordination in the clinopyroxene structure. This observation is supported by vibrational bands characteristic for B-O stretching in BO3 groups in the range 1250-1400 cm(-1) in polarised single crystal FTIR-spectra. Single crystal structure refinements suggest that boron replaces Si at the T site. Combined, these results suggest that boron replacement for Si at the T-site leads to... (More)
To explore mechanisms of B-incorporation in common chain silicates we have investigated synthetic diopside samples produced under boron-saturated conditions by B-11 and Si-29 magic-angle spinning (MAS) NMR and single-crystal NRA, FTIR, EMP and XRD/SREF techniques. Our samples contain 0.14-0.65 wt.% B2O3. NMR reveals that B is predominantly present in trigonal coordination in the clinopyroxene structure. This observation is supported by vibrational bands characteristic for B-O stretching in BO3 groups in the range 1250-1400 cm(-1) in polarised single crystal FTIR-spectra. Single crystal structure refinements suggest that boron replaces Si at the T site. Combined, these results suggest that boron replacement for Si at the T-site leads to disruption of one of the T-O bonds of the nominal clinopyroxene structure resulting in replacement of SiO4 tetrahedra by BO3 groups. Our results show that high concentrations of boron can be incorporated in the nominally boron-free diopside. Elevated B-concentrations in the present calcic clinopyroxenes are accompanied by modifications of the diopside crystal structure involving the breaking of one T-O bond and simultaneous formation of vacancies at the octahedral M2 site. These structural modifications destabilize the structure and constitute thereby limiting factors for incorporating higher boron concentrations in diopside. (C) 2010 Elsevier Ltd. All rights reserved. (Less)
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type
Contribution to journal
publication status
published
subject
in
Geochimica et Cosmochimica Acta
volume
74
issue
19
pages
5672 - 5679
publisher
Elsevier
external identifiers
  • wos:000281423300016
  • scopus:77955921595
ISSN
0016-7037
DOI
10.1016/j.gca.2010.06.033
language
English
LU publication?
yes
id
1a300a5c-01c4-46cc-90d5-320ccb3c4ef4 (old id 1672429)
date added to LUP
2010-09-23 13:51:43
date last changed
2018-05-29 12:06:59
@article{1a300a5c-01c4-46cc-90d5-320ccb3c4ef4,
  abstract     = {To explore mechanisms of B-incorporation in common chain silicates we have investigated synthetic diopside samples produced under boron-saturated conditions by B-11 and Si-29 magic-angle spinning (MAS) NMR and single-crystal NRA, FTIR, EMP and XRD/SREF techniques. Our samples contain 0.14-0.65 wt.% B2O3. NMR reveals that B is predominantly present in trigonal coordination in the clinopyroxene structure. This observation is supported by vibrational bands characteristic for B-O stretching in BO3 groups in the range 1250-1400 cm(-1) in polarised single crystal FTIR-spectra. Single crystal structure refinements suggest that boron replaces Si at the T site. Combined, these results suggest that boron replacement for Si at the T-site leads to disruption of one of the T-O bonds of the nominal clinopyroxene structure resulting in replacement of SiO4 tetrahedra by BO3 groups. Our results show that high concentrations of boron can be incorporated in the nominally boron-free diopside. Elevated B-concentrations in the present calcic clinopyroxenes are accompanied by modifications of the diopside crystal structure involving the breaking of one T-O bond and simultaneous formation of vacancies at the octahedral M2 site. These structural modifications destabilize the structure and constitute thereby limiting factors for incorporating higher boron concentrations in diopside. (C) 2010 Elsevier Ltd. All rights reserved.},
  author       = {Halenius, Ulf and Skogby, Henrik and Eden, Mattias and Nazzareni, Sabrina and Kristiansson, Per and Resmark, Jeppa},
  issn         = {0016-7037},
  language     = {eng},
  number       = {19},
  pages        = {5672--5679},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {Coordination of boron in nominally boron-free rock forming silicates: Evidence for incorporation of BO3 groups in clinopyroxene},
  url          = {http://dx.doi.org/10.1016/j.gca.2010.06.033},
  volume       = {74},
  year         = {2010},
}