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The roedderite-chayesite series from Spanish lamproites: crystal-chemical characterization

  • E. Alietii (a1), M. F. Brigatti (a1), S. Capedri (a1) and L. Poppi (a1)

Abstract

Members of the roedderite-chayesite series in lamproites from Cancarix (SE Spain), crystallized from late magmatic residua under low P H2O, high temperature (∼ 1100°C), oxidizing conditions. They exhibit the following main chemical variations: 0.14 ⩽ Na ⩽ 0.62 atoms per formula unit (apfu); 0.80 ⩽ K⩽ 1.00 apfu; 2.97 ⩽ Mg ⩽ 4.33 apfu; 0.00 ⩽ Fe2+ ⩽ 1.19 apfu; 0.42 ⩽ Fe3+ ⩽ 0.87 apfu; they are hexagonal (10.120 ⩽ a ⩽ 10.135 Å, 14.305 ⩽ c ⩽ 14.326 Å), P6/mcc. The characteristic chemical substitution is: Fe3+ + □ ⇌ Fe2+ + (K+Na)+. Six crystal structures have been refined to 0.020 ⩽ R obs ⩽ 0.026. They have the osumilite/milarite-type structure, with Si entering the double tetrahedral T1 six-membered rings, and Mg and Fe entering both the ring-linking T2 tetrahedra, and the A octahedra. The 12-coordinated C site, located between two double rings of T1 tetrahedra, is occupied mainly by K and subordinately by Na. Furthermore, Na occupies the partially empty nine-fold coordinated B site which occurs both in the ideal (z = 0) and in a split-atom position along the c direction.

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Abraham, K., Gebert, W., Medenbach, O., Schreyer, W. and Hentschel, G. (1983) Eifelite, KNa3Mg4Sii203o, a new mineral of the osumilite group with octahedral sodium. Contrib. Mineral. Petrol, 82, 252–8.
Armbruster, T. (1989) Crystal chemistry of double-ring silicates: structure of roedderite at 100° and 300° K. Eur. J. Mineral, 1, 715–8.
Armbruster, T. and Oberhansli, R. (1988a) Crystal chemistry of double-ring silicates: structural, chemical and optical variation in osumilites. Amer. Mineral, 73, 585–94.
Armbruster, T. and Oberhansli, R. (1988b) Crystal chemistry of double-ring silicates: structure of sugilite and brannockite. Amer. Mineral, 73, 595–600.
Brigatti, M.F., Contini, S., Capedri, S. and Poppi, L. (1993) Crystal chemistry and cation ordering in Pseudobrookite and armalcolite from Spanish lamproites. Eur. J. Mineral, 5, 73–94.
Contini, S., Venturelli, G., Toscani, L., Capedri, S. and Barbieri, M. (1993) Cr-Zr-armalcolite-bearing lamproites of Cancarix, SE Spain. Mineral. Mag., 57, 203–16.
Fleischer, M. and Mandarino, J.A. (1991) Glossary of mineral species. Mineralogical Record, Tucson.
Hawthorne, F.C. and Smith, J.V. (1986) Enumeration of 4-connected 3-dimensional nets and classification of framework silicates. 3D nets based on insertion of 2-connected vertices into 3-connected plane nets. Zeit. Krist., 175, 15–30.
Hawthorne, F.C, Mitsuyoshi, K., Cerny, P., Ball, N., Rossman, G. R. and Grice, J.D. (1991) The crystal chemistry of the milarite-group minerals. Amer. Mineral, 76, 1836–56.
Khan, A.A., Baur, W.H. and Forbes, W.C. (1972) Synthetic magnesian merrihueite, dipotassium penta-magnesium dodecasilicate: tetrahedral mag-nesiosilicate framework crystal structure. Ada Cryst., B28, 267–72.
Liebau, F. (1985) Structural chemistry of silicates. Springer-Verlag, Berlin
North, A.C.T., Phillips, D.C. and Mathews, F.S. (1968) A semi-empirical method of absorption correction. Ada Cryst., A24, 351–9.
Robinson, K., Gibbs, G.V. and Ribbe, P.H. (1971) Quadratic elongation: A quantitative measure of distortion in coordination polyhedra. Science, 172, 567–70.
Sheldrick, G.M. (1976) SHELX-76. Programme for crystal structure determination. Univ. Cambridge, England.
Velde, D., Medenbach, O., Wagner, C. and Schreyer, W. (1989) Chayesite, K(Mg,Fe+2)4Fe3+Si1203o: a new rock forming silicate mineral of the osumilite group from the Moon Canyon (Utah) lamproite. Amer. Mineral, 74, 1368–73.
Wagner, C. and Velde, D. (1986) The mineralogy of K-bearing lamproites. Amer. Mineral, 71, 17–37.
Zoltai, T. (1960) Classification of silicates and other minerals with tetrahedral structures. Amer. Mineral, 45, 960–73.

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