Zonation in tourmaline from granitic pegmatites & the occurrence of tetrahedrally coordinated aluminum and boron in tourmaline
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Date
2008-06
Authors
Lussier, Aaron J.
Journal Title
Journal ISSN
Volume Title
Publisher
Mineralogical Society of Great Britan and Ireland
Mineralogical Society of Great Britan and Ireland
Mineraloigcal Society of America
Mineralogical Association of Canada
Mineralogical Association of Canada
Edizioni Nuova Cultura
Mineralogical Society of Great Britan and Ireland
Mineralogical Society of Great Britan and Ireland
Mineraloigcal Society of America
Mineralogical Association of Canada
Mineralogical Association of Canada
Edizioni Nuova Cultura
Mineralogical Society of Great Britan and Ireland
Abstract
[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms.
[2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.
Description
Keywords
tourmaline, liddicoatite, elbaite, oscillatory zoning, electron-microprobe analysis, liddicoatite-elbaite solid solution, crystal-structure, Mossbauer spectroscopy, Magic-Angle-Spinning Nuclear Magnetic Resonance spectroscopy, Anjanabonoina, Madagascar, Mogok, Myanmar, mushroom tourmaline, wheatsheaf tourmaline, tetrahedrally coordinated Al and B
Citation
Lussier, A.J., Aguiar, P.M., Michaelis, V.K., Kroeker, S., Herwig, S., Abdu, Y. and Hawthorne, F.C. (2008) Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: I. Crystal chemistry by SREF, EMPA, MAS NMR and Mossbauer spectroscopy, Mineralogical Magazine, 72, 747-761.
Lussier, A.J., Hawthorne, F.C., Herwig, S., Abdu, Y., Aguiar, P.M., Michaelis, V.K. and Kroeker, S. (2008) Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: II. Zoning and crystal growth. Mineralogical Magazine, 72, 999-1010
Lussier, A.J., Aguiar, P.M., Michaelis, V.K., Kroeker, S. and Hawthorne, F.C. (2009) The occurrence of tetrahedrally coordinated Al and B in tourmaline: an 11-B and 27-Al MAS NMR study. American Mineralogist, 94, 785-792.
Lussier, A.J., Abudu, Y., Hawthorne, F.C., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. (2011) Oscillatory zoned liddicoatite from Anjanabonoina, Central Madagascar. I. Crystal chemistry and structure by SREF and 11-B and 27-Al MAS NMR spectroscopy. Canadian Mineralogist, 49, 63-88.
Lussier, A.J. and Hawthorne, F.C. (2011) Oscillatory zoned liddicoatite from Anjanabonoina, Central Madagascar. II. Compositional variation and mechanisms of substitution. Canadian Mineralogist, 49, 89-104.
Lussier, A.J., Hawthorne, F.C., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. Elbaite-liddicoatite from Black Rapids glacier, Alaska. Periodico di Mineralogia, 80, 57-73
Lussier, A.J., Hawthorne, F.C., Abdu, Y., Herwig, S., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. The crystal chemistry of 'wheatsheaf' tourmaline from Magok, Myanmar. Mineralogical Magazine, 75, 65-86.
Lussier, A.J., Hawthorne, F.C., Herwig, S., Abdu, Y., Aguiar, P.M., Michaelis, V.K. and Kroeker, S. (2008) Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: II. Zoning and crystal growth. Mineralogical Magazine, 72, 999-1010
Lussier, A.J., Aguiar, P.M., Michaelis, V.K., Kroeker, S. and Hawthorne, F.C. (2009) The occurrence of tetrahedrally coordinated Al and B in tourmaline: an 11-B and 27-Al MAS NMR study. American Mineralogist, 94, 785-792.
Lussier, A.J., Abudu, Y., Hawthorne, F.C., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. (2011) Oscillatory zoned liddicoatite from Anjanabonoina, Central Madagascar. I. Crystal chemistry and structure by SREF and 11-B and 27-Al MAS NMR spectroscopy. Canadian Mineralogist, 49, 63-88.
Lussier, A.J. and Hawthorne, F.C. (2011) Oscillatory zoned liddicoatite from Anjanabonoina, Central Madagascar. II. Compositional variation and mechanisms of substitution. Canadian Mineralogist, 49, 89-104.
Lussier, A.J., Hawthorne, F.C., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. Elbaite-liddicoatite from Black Rapids glacier, Alaska. Periodico di Mineralogia, 80, 57-73
Lussier, A.J., Hawthorne, F.C., Abdu, Y., Herwig, S., Michaelis, V.K., Aguiar, P.M. and Kroeker, S. The crystal chemistry of 'wheatsheaf' tourmaline from Magok, Myanmar. Mineralogical Magazine, 75, 65-86.