Formula
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Intro Page 1 FORMULA: General-purpose mineral analysis recalculation Analytical techniques yield a chemical composition expressed in weig oxides. To make use of mineral analyses, however, we need to recalc some other form. To check the quality of the analysis by examining stoichiometry, or to determine the proportions of end members of sol series, we require cations per formula unit, where the formula unit terms of a fixed number of oxygens. If we want to plot assemblage-c diagrams, we shall need molar proportions of oxides, but these are e from the cation proportions. Follow the column-by-column instructions on the next page to develop spreadsheet application for recalculating weight percents into catio unit.
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Sheet: IntroSheet: WorkingFORMULA: General-purpose mineral analysis recalculationAnalytical techniques yield a chemical composition expressed in weight percentoxides. To make use of mineral analyses, however, we need to recalculate them intosome other form. To check the quality of the analysis by examining thestoichiometry, or to determine the proportions of end members of solid-solutionseries, we require cations per formula unit, where the formula unit is specified interms of a fixed number of oxygens. If we want to plot assemblage-compositiondiagrams, we shall need molar proportions of oxides, but these are easily derivedfrom the cation proportions.Follow the column-by-column instructions on the next page to develop your ownspreadsheet application for recalculating weight percents into cations per formulaunit.FORMULA: General-purpose mineral analysis recalculationIn column B, enter oxygens in formula unit, and weight % of each oxide in the analysisIn column C, divide by the molecular weight given in column H, yielding cationproportions.Now multiply column C by the number of oxygens associated with eachcation in the oxide (i.e. by half the charge on the cation)Finally, normalise the cation proportions in column C to theOxygenscorrect oxygen total. The factor is in formula24.0(oxygens in formula)/(total beneath column D)Wt %CationOxygenCationsOxideMol wtChargeoxidepropspropsp.f.u.nameper cationon cationSiO251.730.86087535363621231.72175070727242457.8348648440389566SiO2TiO20.00.00.00.0TiO2Al2O31.510.0296252697665293320.0444379046497940.2696208964614355Al2O3Cr2O30.00.00.00.0Cr2O3Fe2O30.00.00.00.0Fe2O3FeO23.320.324565066109951340.324565066109951342.953881087810331FeOMnO0.360.0050747110234000560.0050747110234000560.04618517050459742MnOMgO8.690.215525793650793630.215525793650793631.9615098243035205MgOCaO11.850.21130527817403710.21130527817403711.923098725422723CaONa2O0.210.00677616082088348250.00338808041044174130.06167014071067134Na2O30.9911.0K2O0.00.00.00.0K2OH2O2.00.222024866785079960.111012433392539982.0206581776668524H2O9.0081.0Totals99.669999999999992.637059974683382317.071488866919086
