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| Home > Publications database > Thermal and combined high-temperature and high-pressure behavior of a natural intermediate scapolite |
| Journal Article | FZJ-2023-04485 |
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2024
GeoScienceWorld
Alexandria, Va.
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Please use a persistent id in citations: doi:10.2138/am-2023-8962 doi:10.34734/FZJ-2023-04485
Abstract: A natural intermediate member of the scapolite solid solution (Me$_{47}$; experimental chemical formula: (Na$_{1.86}$Ca$_{1.86}$K$_{0.23}$Fe$_{0.01}$)(Al$_{4.36}$Si$_{7.64}$)O$_{24}$[Cl$_{0.48}$(CO$_3$)$_{0.48}$(SO$_4$)$_{0.01}$]), with the unusual I4/m space group, has been studied at various temperatures and combined high-$T$ and high-$P$ by means of in situ single-crystal and powder X-ray diffraction, at both conventional and synchrotron sources. In addition, single-crystal neutron diffraction data were collected at ambient-T and 685 °C. A fit of the experimental V-T data with a thermal equation of state yielded a calculated thermal expansion coefficient at ambient conditions: $α_{V25°C} = 1/V_0·(∂V/∂T)_{P,25°C} = 1.74(3)·10^{-5}$ K$^{-1}$. A comparative analysis of the elastic behavior of scapolite based on this study and other high-$T$ XRD data reported in the literature suggests that a thorough re-investigation of the different members of the marialite-meionite solid solution is needed to fully understand the role of crystal chemistry on the thermal behavior of these complex non-binary solid solutions. The experimental data obtained within the full temperature range of analysis at ambient pressure confirm that the investigated sample always preserves the I4/m space group, and possible implications on the metastability of I4/m intermediate scapolite are discussed. Neutron diffraction data show that no significant Si and Al re-arrangement among the T sites occurs between 25 and 685 °C. The combined high-$T$ and high-$P$ data show that at 650 °C and between 10.30(5) and 10.71(5) GPa a phase transition towards a triclinic polymorph occurs, with a positive Clapeyron slope (i.e., $dP/dT > 0$). A comprehensive description of the atomic-scale structure deformation mechanisms induced by temperature and/or pressure, including those leading to structural instability, is provided based on single-crystal structure refinements.
Keyword(s): Earth, Environment and Cultural Heritage (1st) ; Crystallography (2nd) ; Geosciences (2nd) ; Chemistry (2nd)
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