Boralsilite, Al16B6Si2O37, and "boron-mullite:" Compositional variations and associated phases in experiment and nature

Graetsch, Heribert A.; Pöter, Birgit; Yates, Martin G.; Buick, Ian S.; Bernhardt, Heinz-Jürgen; Schreyer, Werner; Werding, G.; Carson, Chris; Clarke, Graeme

doi:10.2138/am.2008.2571

Cited by 36 publications

(24 citation statements)

References 27 publications

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“…Systematic extinctions of hkl reflections with h + k ≠ 2n indicated a C-centered Bravais type. These parameters closely resemble the metrical parameters of boralsilite (Grew et al 1998), Al 16 B 6 Si 2 O 37 , described in the monoclinic space group C2/m with a = 14.77 Å, b = 5.57 Å, c = 15.08 Å, and β = 91.96° (Peacor et al 1999;Grew et al 2008) also represented by its synthetic B-rich counterpart (Grew et al 2008). Preliminary structure refinements using the atomic parameters of boralsilite gave a reasonable fit with the observed diffraction data and confirmed the close relationship of boralsilite with the aluminum borate studied here.…”

Section: Resultssupporting

confidence: 58%

Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite

Fischer

Kahlenberg

Voll

et al. 2008

American Mineralogist

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The crystal structure of Al 4 B 2 O 9 , synthesized from Al(NO) 3 ·9H 2 O and B(OH) 3 via a sol-gel process, is studied and characterized by Rietveld refinements and grid search analyses combined with 11 B and 27 Al MAS NMR spectroscopy. The aluminum borate with a unit-cell composition of Al 32 B 16 O 72 is closely related to the boralsilite (Al 32 B 12 Si 4 O 74 ) structure with Si replaced by B and to mullite (Al 4+2x Si 2-2x O 10-x ). It crystallizes in the monoclinic space group C2/m, a = 14.8056(7) Å, b = 5.5413(2) Å, c = 15.0531(6) Å, β = 90.913(2)°, Z = 8 for Al 4 B 2 O 9 . The main structural units are isolated chains of edge-sharing AlO 6 -octahedra running parallel to b that is a characteristic feature of the mullite-type crystal structures. The octahedral chains are crosslinked by AlO 4 , AlO 5 , BO 3 , and BO 4 groups with two B atoms and one O atom (O5') disordered on interstitial positions. 27 Al and 11 B NMR studies confirm the presence of sixfold (octahedral), fivefold, and fourfold (tetrahedral) coordinated Al (sixfold:[fourfold + fivefold] = ~50%:50%) and of threefold and fourfold coordinated B (~80%:20%).

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Section: Resultssupporting

confidence: 58%

Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite

Fischer

Kahlenberg

Voll

et al. 2008

American Mineralogist

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“…Black filled circles are the compositions investigated in this work. Three phases with distinct compositions that contain Si have been investigated so far: Boromullite [12,13], boralsilite [14], and Al 8 Si 2 B 2 O 19 [14]. 58 to 12082u was applied and for Mo radiation scans were performed in the range of 5-6082u with a measuring time of 15 s/ step.…”

Section: Methodsmentioning

confidence: 99%

Boron mullite: Formation and basic characterization

Lührs

Fischer

Schneider

2012

Materials Research Bulletin

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“…The (sub)microfibrous character of holtite is a possible cause of the low analytical totals. Grew et al (2008) attributed low totals for analyses of finely porous material to contamination from epoxy filling the pores; similarly, epoxy could have filled the gaps between the very fine fibres of holtite. In addition, we suspect that the data reduction routines are unable to correct completely for the effect of As, Sb, and Ta Data collection and refinement parameters for the single-crystal X-ray experiments are summarized in Table 2, positional parameters in Table 3 and bond lengths in Table 4.…”

Section: Resultsmentioning

confidence: 99%

The crystal chemistry of holtite

Groat¹,

Evans²,

Pieczka³

et al. 2009

Mineral. mag.

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Sb 3+ ,As 3+ ) S3 O 12 (O,OH,&) S3 , is a member of the dumortierite group that has been found in pegmatite, or alluvial deposits derived from pegmatite, at three localities: Greenbushes, Western Australia; Voron'i Tundry, Kola Peninsula, Russia; and Szklary, Lower Silesia, Poland. Holtite can contain >30 wt.% Sb 2 O 3 , As 2 O 3 , Ta 2 O 5 , Nb 2 O 5 , and TiO 2 (taken together), but none of these constituents is dominant at a crystallographic site, which raises the question whether this mineral is distinct from dumortierite. The crystal structures of four samples from the three localities have been refined to R 1 = 0.02À0.05. The results show dominantly: Al, Ta, and vacancies at the Al(1) position; Al and vacancies at the Al(2), (3) and (4) sites; Si and vacancies at the Si positions; and Sb, As and vacancies at the Sb sites for both Sb-poor (holtite I) and Sb-rich (holtite II) specimens. Although charge-balance calculations based on our single-crystal structure refinements suggest that essentially no water is present, Fourier transform infrared spectra confirm that some OH is present in the three samples that could be measured. By analogy with dumortierite, the largest peak at 3505À3490 cm À1 is identified with OH at the O(2) and O(7) positions. The single-crystal X-ray refinements and FTIR results suggest the following general formula for holtite: Al 7À[5x+y+z]/3 (Ta,Nb) x & [2x+y+z]/3 BSi 3Ày (Sb,As) y O 18ÀyÀz (OH) z , where x is the total number of pentavalent cations, y is the total amount of Sb + As, and z 4 y is the total amount of OH. Comparison with the electron microprobe compositions suggests the following approximate general formulae Al 5.83 (Ta,Nb) 0.50 & 0.67 BSi 2.50 (Sb,As) 0.50 O 17.00 (OH) 0.50 and Al 5.92 (Ta,Nb) 0.25 & 0.83 BSi 2.00 (Sb,As) 1.00 O 16.00 (OH) 1.00 for holtite I and holtite II respectively. However, the crystal structure refinements do not indicate a fundamental difference in cation ordering that might serve as a criterion for recognizing the two holtites as distinct species, and anion compositions are also not sufficiently different. Moreover, available analyses suggest the possibility of a continuum in the Si/(Sb + As) ratio between holtite I and dumortierite, and at least a partial continuum between holtite I and holtite II. We recommend that use of the terms holtite I and holtite II be discontinued.

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Boralsilite, Al16B6Si2O37, and "boron-mullite:" Compositional variations and associated phases in experiment and nature

Cited by 36 publications

References 27 publications

Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite

Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite

Boron mullite: Formation and basic characterization

The crystal chemistry of holtite

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