Boromullite, Al2BSi2O19, a new mineral from granulite-facies metapelites, Mount Stafford, central Australia: A natural analogue of a synthetic "boron-mullite"

Ian S. Buick, Edward S. Grew, Thomas Armbruster, Olaf Medenbach, Martin G. Yates, Gray Edward Bebout, Geoffrey L. Clarke

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Boromullite is a new mineral corresponding to a 1:1 polysome composed of Al5BO9 and Al2SiO5 modules. Electron-microprobe analysis of the holotype prism is SiO2 19.01(l.12), TiO2 0.01(0.02), B2O3 6.52(0.75), Al2O3 74.10(0.95), MgO 0.07(0.03), CaO 0.00(0.02), MnO 0.01(0.04), FeO 0.40(0.08), Sum 100.12 wt.%, which gives Mg0.01 Fe0.03 Al8.88 Si1.93 B1.14 O18.94 (normalised to 12 cations), ideally Al9BSi2O19. Overall, in the type specimen, it ranges in composition from Mg0.01 Fe0.03 Al8.72 Si2.44 B0.80 O19.20 to Mg0.01 Fe0.03 Al9.22 Si1.38 B1.35 O18.67. Single-crystal X-ray diffraction gives orthorhombic symmetry, Cmc21, a 5.7168(19) Å, b 15.023(5) Å, c 7.675(3) Å, V 659.2(7) Å3, calculated density 3.081 g/cm3, Z = 2. The refined structure model indicates two superimposed modules present in equal proportions in the holotype prism. Module 1 has the topology and stoichiometry of sillimanite and carries all the Si, whereas module 2 is a type of mullite defect structure in which Si is replaced by B in triangular coordination and by Al in tetrahedral coordination, i.e., Al5BO9. The strongest lines in the powder pattern [d in Å, Imeas.), (hkl)] are 5.37(50) (021), 3.38(100) (022, 041), 2.67 (60) (042), 2.51(60) (221, 023), 2.19(80) (222), 2.11(50) (043), 1.512(90) (263). Boromullite is colourless and transparent, biaxial (+), nx 1.627(1), ny 1.634(1), nz 1.649(1) (589 nm). 2Vz (meas) = 57(2)°, 2Vz (calc) = 69(12)°. In the type specimen boromullite tends to form prisms or bundles of prisms up to 0.4 mm long, typically as fringes or overgrowths on aggregates of sillimanite or as narrow overgrowths around embayed werdingite prisms. In other samples boromullite and sillimanite are intergrown on a fine scale (from < 1 μm to > 10 μm). Sekaninaite-cordierite, potassium feldspar, biotite, werdingite and its Fe-dominant analogue, hercynite, and ilmenite are other commonly associated minerals, whereas ominelite-grandidierite, plagioclase, andalusite, and tourmaline are much subordinate. The most widespread accessories are monazite-(Ce), an apatite-group mineral and zircon. Boromullite formed during anatexis of B-rich pelitic rocks under granulite facies conditions (810 °C ≈ T ≥ 775-785 °C, P = 3.3-4 kbar), possibly due to a shift in bulk composition to lower SiO2 and B2O3 contents associated with melt extraction. The assemblage boromullite + cordierite + sillimanite lies at lower SiO2 and B2O3 contents than the assemblage werdingite + cordierite + sillimanite and thus a decrease in SiO2 and B2O3 leads to the replacement of werdingite by boromullite, consistent with textural relations.

Original languageEnglish
Pages (from-to)935-950
Number of pages16
JournalEuropean Journal of Mineralogy
Volume20
Issue number5
DOIs
Publication statusPublished - Sep 2008
Externally publishedYes

Fingerprint

natural analog
porcellanite
Boron
metapelite
new mineral
sillimanite
granulite facies
Prisms
boron
Minerals
cordierite
type specimen
hercynite
Apatites
andalusite
anatexis
Defect structures
tourmaline
Accessories
Crystal symmetry

Keywords

  • Anatexis
  • Australia
  • Boromullite
  • Boron
  • Crystal structure
  • Electron microprobe
  • Granulite facies
  • New mineral

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Boromullite, Al2BSi2O19, a new mineral from granulite-facies metapelites, Mount Stafford, central Australia : A natural analogue of a synthetic "boron-mullite". / Buick, Ian S.; Grew, Edward S.; Armbruster, Thomas; Medenbach, Olaf; Yates, Martin G.; Edward Bebout, Gray; Clarke, Geoffrey L.

In: European Journal of Mineralogy, Vol. 20, No. 5, 09.2008, p. 935-950.

Research output: Contribution to journalArticle

Buick, Ian S. ; Grew, Edward S. ; Armbruster, Thomas ; Medenbach, Olaf ; Yates, Martin G. ; Edward Bebout, Gray ; Clarke, Geoffrey L. / Boromullite, Al2BSi2O19, a new mineral from granulite-facies metapelites, Mount Stafford, central Australia : A natural analogue of a synthetic "boron-mullite". In: European Journal of Mineralogy. 2008 ; Vol. 20, No. 5. pp. 935-950.
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title = "Boromullite, Al2BSi2O19, a new mineral from granulite-facies metapelites, Mount Stafford, central Australia: A natural analogue of a synthetic {"}boron-mullite{"}",
abstract = "Boromullite is a new mineral corresponding to a 1:1 polysome composed of Al5BO9 and Al2SiO5 modules. Electron-microprobe analysis of the holotype prism is SiO2 19.01(l.12), TiO2 0.01(0.02), B2O3 6.52(0.75), Al2O3 74.10(0.95), MgO 0.07(0.03), CaO 0.00(0.02), MnO 0.01(0.04), FeO 0.40(0.08), Sum 100.12 wt.{\%}, which gives Mg0.01 Fe0.03 Al8.88 Si1.93 B1.14 O18.94 (normalised to 12 cations), ideally Al9BSi2O19. Overall, in the type specimen, it ranges in composition from Mg0.01 Fe0.03 Al8.72 Si2.44 B0.80 O19.20 to Mg0.01 Fe0.03 Al9.22 Si1.38 B1.35 O18.67. Single-crystal X-ray diffraction gives orthorhombic symmetry, Cmc21, a 5.7168(19) {\AA}, b 15.023(5) {\AA}, c 7.675(3) {\AA}, V 659.2(7) {\AA}3, calculated density 3.081 g/cm3, Z = 2. The refined structure model indicates two superimposed modules present in equal proportions in the holotype prism. Module 1 has the topology and stoichiometry of sillimanite and carries all the Si, whereas module 2 is a type of mullite defect structure in which Si is replaced by B in triangular coordination and by Al in tetrahedral coordination, i.e., Al5BO9. The strongest lines in the powder pattern [d in {\AA}, Imeas.), (hkl)] are 5.37(50) (021), 3.38(100) (022, 041), 2.67 (60) (042), 2.51(60) (221, 023), 2.19(80) (222), 2.11(50) (043), 1.512(90) (263). Boromullite is colourless and transparent, biaxial (+), nx 1.627(1), ny 1.634(1), nz 1.649(1) (589 nm). 2Vz (meas) = 57(2)°, 2Vz (calc) = 69(12)°. In the type specimen boromullite tends to form prisms or bundles of prisms up to 0.4 mm long, typically as fringes or overgrowths on aggregates of sillimanite or as narrow overgrowths around embayed werdingite prisms. In other samples boromullite and sillimanite are intergrown on a fine scale (from < 1 μm to > 10 μm). Sekaninaite-cordierite, potassium feldspar, biotite, werdingite and its Fe-dominant analogue, hercynite, and ilmenite are other commonly associated minerals, whereas ominelite-grandidierite, plagioclase, andalusite, and tourmaline are much subordinate. The most widespread accessories are monazite-(Ce), an apatite-group mineral and zircon. Boromullite formed during anatexis of B-rich pelitic rocks under granulite facies conditions (810 °C ≈ T ≥ 775-785 °C, P = 3.3-4 kbar), possibly due to a shift in bulk composition to lower SiO2 and B2O3 contents associated with melt extraction. The assemblage boromullite + cordierite + sillimanite lies at lower SiO2 and B2O3 contents than the assemblage werdingite + cordierite + sillimanite and thus a decrease in SiO2 and B2O3 leads to the replacement of werdingite by boromullite, consistent with textural relations.",
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author = "Buick, {Ian S.} and Grew, {Edward S.} and Thomas Armbruster and Olaf Medenbach and Yates, {Martin G.} and {Edward Bebout}, Gray and Clarke, {Geoffrey L.}",
year = "2008",
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language = "English",
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TY - JOUR

T1 - Boromullite, Al2BSi2O19, a new mineral from granulite-facies metapelites, Mount Stafford, central Australia

T2 - A natural analogue of a synthetic "boron-mullite"

AU - Buick, Ian S.

AU - Grew, Edward S.

AU - Armbruster, Thomas

AU - Medenbach, Olaf

AU - Yates, Martin G.

AU - Edward Bebout, Gray

AU - Clarke, Geoffrey L.

PY - 2008/9

Y1 - 2008/9

N2 - Boromullite is a new mineral corresponding to a 1:1 polysome composed of Al5BO9 and Al2SiO5 modules. Electron-microprobe analysis of the holotype prism is SiO2 19.01(l.12), TiO2 0.01(0.02), B2O3 6.52(0.75), Al2O3 74.10(0.95), MgO 0.07(0.03), CaO 0.00(0.02), MnO 0.01(0.04), FeO 0.40(0.08), Sum 100.12 wt.%, which gives Mg0.01 Fe0.03 Al8.88 Si1.93 B1.14 O18.94 (normalised to 12 cations), ideally Al9BSi2O19. Overall, in the type specimen, it ranges in composition from Mg0.01 Fe0.03 Al8.72 Si2.44 B0.80 O19.20 to Mg0.01 Fe0.03 Al9.22 Si1.38 B1.35 O18.67. Single-crystal X-ray diffraction gives orthorhombic symmetry, Cmc21, a 5.7168(19) Å, b 15.023(5) Å, c 7.675(3) Å, V 659.2(7) Å3, calculated density 3.081 g/cm3, Z = 2. The refined structure model indicates two superimposed modules present in equal proportions in the holotype prism. Module 1 has the topology and stoichiometry of sillimanite and carries all the Si, whereas module 2 is a type of mullite defect structure in which Si is replaced by B in triangular coordination and by Al in tetrahedral coordination, i.e., Al5BO9. The strongest lines in the powder pattern [d in Å, Imeas.), (hkl)] are 5.37(50) (021), 3.38(100) (022, 041), 2.67 (60) (042), 2.51(60) (221, 023), 2.19(80) (222), 2.11(50) (043), 1.512(90) (263). Boromullite is colourless and transparent, biaxial (+), nx 1.627(1), ny 1.634(1), nz 1.649(1) (589 nm). 2Vz (meas) = 57(2)°, 2Vz (calc) = 69(12)°. In the type specimen boromullite tends to form prisms or bundles of prisms up to 0.4 mm long, typically as fringes or overgrowths on aggregates of sillimanite or as narrow overgrowths around embayed werdingite prisms. In other samples boromullite and sillimanite are intergrown on a fine scale (from < 1 μm to > 10 μm). Sekaninaite-cordierite, potassium feldspar, biotite, werdingite and its Fe-dominant analogue, hercynite, and ilmenite are other commonly associated minerals, whereas ominelite-grandidierite, plagioclase, andalusite, and tourmaline are much subordinate. The most widespread accessories are monazite-(Ce), an apatite-group mineral and zircon. Boromullite formed during anatexis of B-rich pelitic rocks under granulite facies conditions (810 °C ≈ T ≥ 775-785 °C, P = 3.3-4 kbar), possibly due to a shift in bulk composition to lower SiO2 and B2O3 contents associated with melt extraction. The assemblage boromullite + cordierite + sillimanite lies at lower SiO2 and B2O3 contents than the assemblage werdingite + cordierite + sillimanite and thus a decrease in SiO2 and B2O3 leads to the replacement of werdingite by boromullite, consistent with textural relations.

AB - Boromullite is a new mineral corresponding to a 1:1 polysome composed of Al5BO9 and Al2SiO5 modules. Electron-microprobe analysis of the holotype prism is SiO2 19.01(l.12), TiO2 0.01(0.02), B2O3 6.52(0.75), Al2O3 74.10(0.95), MgO 0.07(0.03), CaO 0.00(0.02), MnO 0.01(0.04), FeO 0.40(0.08), Sum 100.12 wt.%, which gives Mg0.01 Fe0.03 Al8.88 Si1.93 B1.14 O18.94 (normalised to 12 cations), ideally Al9BSi2O19. Overall, in the type specimen, it ranges in composition from Mg0.01 Fe0.03 Al8.72 Si2.44 B0.80 O19.20 to Mg0.01 Fe0.03 Al9.22 Si1.38 B1.35 O18.67. Single-crystal X-ray diffraction gives orthorhombic symmetry, Cmc21, a 5.7168(19) Å, b 15.023(5) Å, c 7.675(3) Å, V 659.2(7) Å3, calculated density 3.081 g/cm3, Z = 2. The refined structure model indicates two superimposed modules present in equal proportions in the holotype prism. Module 1 has the topology and stoichiometry of sillimanite and carries all the Si, whereas module 2 is a type of mullite defect structure in which Si is replaced by B in triangular coordination and by Al in tetrahedral coordination, i.e., Al5BO9. The strongest lines in the powder pattern [d in Å, Imeas.), (hkl)] are 5.37(50) (021), 3.38(100) (022, 041), 2.67 (60) (042), 2.51(60) (221, 023), 2.19(80) (222), 2.11(50) (043), 1.512(90) (263). Boromullite is colourless and transparent, biaxial (+), nx 1.627(1), ny 1.634(1), nz 1.649(1) (589 nm). 2Vz (meas) = 57(2)°, 2Vz (calc) = 69(12)°. In the type specimen boromullite tends to form prisms or bundles of prisms up to 0.4 mm long, typically as fringes or overgrowths on aggregates of sillimanite or as narrow overgrowths around embayed werdingite prisms. In other samples boromullite and sillimanite are intergrown on a fine scale (from < 1 μm to > 10 μm). Sekaninaite-cordierite, potassium feldspar, biotite, werdingite and its Fe-dominant analogue, hercynite, and ilmenite are other commonly associated minerals, whereas ominelite-grandidierite, plagioclase, andalusite, and tourmaline are much subordinate. The most widespread accessories are monazite-(Ce), an apatite-group mineral and zircon. Boromullite formed during anatexis of B-rich pelitic rocks under granulite facies conditions (810 °C ≈ T ≥ 775-785 °C, P = 3.3-4 kbar), possibly due to a shift in bulk composition to lower SiO2 and B2O3 contents associated with melt extraction. The assemblage boromullite + cordierite + sillimanite lies at lower SiO2 and B2O3 contents than the assemblage werdingite + cordierite + sillimanite and thus a decrease in SiO2 and B2O3 leads to the replacement of werdingite by boromullite, consistent with textural relations.

KW - Anatexis

KW - Australia

KW - Boromullite

KW - Boron

KW - Crystal structure

KW - Electron microprobe

KW - Granulite facies

KW - New mineral

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