Crystal chemistry of strontian soda melilite from nephelinite lava of Mt. Etinde, Cameroon
Bindi, Luca; Bonazzi, Paola; Fitton, J. Godfrey
European Journal of Mineralogy Volume 13 Number 1 (2001), p. 121 - 125
published: Jan 31, 2001
ArtNo. ESP147051301012, Price: 29.00 €
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. and (Ca0.83Sr0.45Na0.72) (Mg0.20Fe2+0.06Mn0.03Zn0.01Al0.45Fe3+0.24Ti0.02)(Si1.99Al0.01)O7.00, for ET1 and ET2 respectively. Lattice parameters are: a = 7.754(1), c = 5.101(1) Å 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.