Substitution of ‘small’ divalent cations (e.g. Mg) for Si and Al in the nepheline tetrahedral framework: 1. Calculation of atomic formulae and stoichiometry parameters

A recent review paper on nepheline solid solutions dealt mainly with sodic varieties from nepheline syenites and differentiated alkali basaltic sills. Excel spreadsheets were provided for recalculating cell formulae in terms of the stoichiometric parameters ΔAl cavity cation charge and ΔT framework charge and molecular percentages of the end-members Ne, Ks, Ca-nepheline and excess Si (Q xs ). Small amounts of tetrahedral divalent species (usually