LOCAL CA-MG DISTRIBUTION OF MG-RICH PYROPE-GROSSULAR GARNETS SYNTHESIZED AT DIFFERENT TEMPERATURES REVEALED BY 29SI MAS NMR SPECTROSCOPY
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dc.contributor.author | Bosenick A. | |
dc.contributor.author | Geiger C.A. | |
dc.contributor.author | Phillips B.L. | |
dc.date.accessioned | 2021-01-15T04:55:25Z | |
dc.date.available | 2021-01-15T04:55:25Z | |
dc.date.issued | 1999 | |
dc.identifier | https://elibrary.ru/item.asp?id=31772994 | |
dc.identifier.citation | American Mineralogist, 1999, 84, 9, 1422-1432 | |
dc.identifier.issn | 0003-004X | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/23091 | |
dc.description.abstract | Pyrope-grossular solid solutions, (Mg,Ca) 3 Al 2 Si 3 O 12 , of composition Py 85 Gr 25 and Py 75 Gr 25 were synthesized at 1000, 1200, and 1400 degrees C and 30 kbars in a piston-cylinder device. The synthetic garnets were characterized using optical, microprobe, and X-ray methods and their Ca-Mg distributions were investigated using 29 Si MAS NMR spectroscopy. The syntheses produced 100% garnet except for those undertaken at 1000 degrees C, where small amounts (up to 3%) of clinopyroxene were present. X-ray powder refinements showed differences up to 0.01 Aa in the unit-cell dimension of the garnets synthesized at the three different temperatures. A general decrease of the X-ray diffraction line widths with increasing synthesis temperature is observed. The 29 Si NMR spectra of Py 85 Gr 15 show little change as a function of synthesis temperature. In the spectra of Py 75 Gr 25 small but measurable changes in the relative peak intensities, depending upon synthesis temperature, were observed with a more random cation distribution corresponding to a higher synthesis temperature. None of the garnets investigated has a completely random Ca-Mg distribution. The reduction in configurational entropy compared to the disordered state is estimated to be less than 2 J/mol.K. | |
dc.title | LOCAL CA-MG DISTRIBUTION OF MG-RICH PYROPE-GROSSULAR GARNETS SYNTHESIZED AT DIFFERENT TEMPERATURES REVEALED BY 29SI MAS NMR SPECTROSCOPY | |
dc.type | Статья |
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