The crystal structure and chemical composition of two crystals (labelled ET1 and ET2) of strontian soda melilite from Mt. Etinde, Cameroon, are investigated. Quantitative analysis leads to the following formulae: (Ca0.84Sr0.45Na0.71)(Mg0.19Fe2+0.06Mn0.03Zn0.02Al0.46Fe3+0.23Ti0.01)(Si1.99Al0.01)O7.00and (Ca0.83Sr0.45Na0.72) (Mg0.20Fe2+0.06Mn0.01Zn0.01Al0.45Fe3+0.24Ti0.02)(Si1.99Al0.01)O7.00, for ETl and ET2 respectively. Lattice parameters are: a = 7.754(1), c = 5.101(1) A for ET1 and a = 7.764(1), c = 5.095(1) Å for ET2. The structure is refined up to Rall = 2.64 and 2.78 %, respectively, using 430 independent reflections. Substitution of Sr for Ca causes sufficient modification of the tetrahedral layer to destabilize the incommensurate modulated structure.

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