An Excel spreadsheet to recast analyses of garnet into end-member components, and a synopsis of the crystal chemistry of natural silicate garnets ?
A Microsoft Excel spreadsheet has been programmed that allows users to calculate with ease the molar proportions of garnet end-members from chemical analyses. Recent advances in the understanding of the crystal chemistry of natural garnets, especially of the Ti-bearing garnets, are used to evaluate 29 end-members (15 species and 14 hypothetical end-members) for each analysis. The amounts of Fe2+ and Fe3+ (and Mn3+, if necessary) are calculated by stoichiometric constraints if these quantities have not been measured. The input data can include: SiO2, TiO2, ZrO2, SnO2, Y2O3, Al2O3, Sc2O3, Cr2O3, V2O3, FeO, Fe2O3, MnO, MgO, CaO, Na2O, H2O+ and F. The spreadsheet can be used with large data sets (up to 100 analyses at a time), and is accompanied by results calculated for 470 garnet analyses taken from the literature. The spreadsheet employs a simple scoring algorithm to measure the quality of a garnet analysis. The propagation of error from the input chemical data to the calculation of end-member proportions is also discussed briefly.
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