The scapolite series of minerals represents a complex non-binary solid solution, which end members are: marialite [Na4Al3Si9O24Cl], meionite [Ca4Al6Si6O24CO3] and silvialite [Ca4Al6Si6O24SO4]. The members which composition falls on the marialite-meionite joint appears to be the most common in natural occurrences [1,2]. The members close to marialite on one side and to meionite on the other side, are usually reported to crystallize in the tetragonal I4/m space group, whereas intermediate scapolites are usually found in the primitive space group P42/n. In this study, we report a scapolite sample from Madagascar, which composition falls between those of the end-members marialite an meionite: (Na1.86Ca1.86K0.23Fe0.01)(Al4.36Si7.64)O24[Cl0.48(CO3)0.48(SO4)0.01]. Based on both X-ray and neutron single-crystal diffraction data, an anomalous I-centered lattice (I4/m space group) is observed. This unusual symmetry for an intermediate scapolite, may be assigned to the presence of anti-phase domains too small to be detected by diffraction techniques. In situ high-T X-ray diffraction investigations show that the I4/m space group is observed to be stable at least up to 1000 °C. [1] D.K. Teerstra, B.L. Sheriff Chem. Geol. 1997, 136, 233 [2] E. Sokolova, F.C. Hawthorne Can. Mineral. 2008, 46, 1527.
Unusual symmetry of intermediate scapolite / P. Lotti, D. Comboni, G.D. Gatta. ((Intervento presentato al convegno Il tempo del pianeta Terra e il tempo dell'uomo: le geoscienze tra passato e futuro : Congresso congiunto SIMP-SGI-SOGEI tenutosi a Parma nel 2019.
Unusual symmetry of intermediate scapolite
P. Lotti
Primo
;D. ComboniPenultimo
;G.D. GattaUltimo
2019
Abstract
The scapolite series of minerals represents a complex non-binary solid solution, which end members are: marialite [Na4Al3Si9O24Cl], meionite [Ca4Al6Si6O24CO3] and silvialite [Ca4Al6Si6O24SO4]. The members which composition falls on the marialite-meionite joint appears to be the most common in natural occurrences [1,2]. The members close to marialite on one side and to meionite on the other side, are usually reported to crystallize in the tetragonal I4/m space group, whereas intermediate scapolites are usually found in the primitive space group P42/n. In this study, we report a scapolite sample from Madagascar, which composition falls between those of the end-members marialite an meionite: (Na1.86Ca1.86K0.23Fe0.01)(Al4.36Si7.64)O24[Cl0.48(CO3)0.48(SO4)0.01]. Based on both X-ray and neutron single-crystal diffraction data, an anomalous I-centered lattice (I4/m space group) is observed. This unusual symmetry for an intermediate scapolite, may be assigned to the presence of anti-phase domains too small to be detected by diffraction techniques. In situ high-T X-ray diffraction investigations show that the I4/m space group is observed to be stable at least up to 1000 °C. [1] D.K. Teerstra, B.L. Sheriff Chem. Geol. 1997, 136, 233 [2] E. Sokolova, F.C. Hawthorne Can. Mineral. 2008, 46, 1527.File | Dimensione | Formato | |
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