Gem pargasite and fluoro-pargasite from Mogok, Myanmar: crystal-structure refinement, IR and short-range O-D

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Marco E. Ciriotti
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Gem pargasite and fluoro-pargasite from Mogok, Myanmar: crystal-structure refinement, IR and short-range O-D

Messaggio da Marco E. Ciriotti » sab 15 set, 2018 12:12

Prossima pubblicazione.

Referenza:
▪ Day, M.C., Hawthorne, F.C., Susta, U., Della Ventura, G., Harlow, G.E. (2018): Gem amphiboles from Mogok, Myanmar: crystal-structure refinement, infrared spectroscopy and short-range order-disorder in gem pargasite and fluoro-pargasite. Mineralogical Magazine, 82, (in press).

Abstract:
The crystal structures of six gem-quality pargasites and fluoro-pargasites from Mogok, Myanmar, space group C2/m, Z = 2, have been refined to R1 indices of 2.20–2.78 % using MoKα X-radiation. The unit formulae were calculated from the results of electron-microprobe analysis, and were used with the refined site-scattering values and the observed mean bond-lengths to assign site populations. TAl occurs at both the T(1) and T(2) sites but is strongly ordered at T(1). [6]Al is partly disordered over the M(2) and M(3) sites but does not occur at the M(1) site. ANa is split between the A(2) and A(m) sites and K occurs at the A(m) site. The infrared spectra in the principal (OH)-stretching region were measured and the fine structure was fit to component bands. The component bands were assigned to short-range ion arrangements over the configuration symbol M(1)M(1)M(3)–O(3)–A–O(3):T(1)T(1) using the refined site-populations and the expected frequencies from previously assigned spectra in more simple amphibole compositions, and correspond to the local arrangements: (1) MgMgMg–OH–Na–OH:SiAl; (2) MgMgMg–OH–Na–F:SiAl; (3) MgMgAl–OH–Na–OH:SiAl and (4) MgMgAl–OH–Na–F:SiAl.
Marco E. Ciriotti

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