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 Fe(2+) and Fe(3+) (and Mn(3+), if necessary) are Calculated by stoichiometric constraints if these quantities have not been measured. The input data can include: SiO(2), TiO(2), ZrO(2), SnO(2), Y(2)O(3), Al(2)O(3), SC(2)O(3), Cr(23), V(2)O(3), FeO, Fe(2)O(3), MnO, MgO, CaO, Na(2)O, H(2)O(+) and F. The spreadsheet can be used with large data sets (Lip 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. (c) 2008 Elsevier Ltd. All rights reserved.
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