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| Titel |
Cancrinite-group minerals behavior at non-ambient conditions |
| VerfasserIn |
Paolo Lotti, G. Diego Gatta, Volker Kahlenberg, Marco Merlini, Matteo Alvaro, Fernando Camara |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089860
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| Publikation (Nr.) |
 EGU/EGU2014-4073.pdf |
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| Zusammenfassung |
| Cancrinite-group minerals occur in the late stages of alkaline (SiO2)-undersaturated
magmatism and in related effusive or contact rocks. So far only few studies have been
devoted to the description of the thermo-elastic behavior, phase-stability and P /T -structure
evolution (at the atomic scale) of this mineral group.
Cancrinite-group minerals have an open-framework structure characterized by the
[CAN]-topology. The [CAN]-framework shows large 12-ring channels, parallel to the c
crystallographic axis, bound by columns of cages, the so-called can units. While very limited
chemical variation is observed in the framework composition (the composition is almost
always [Si6Al6O24]) a remarkable chemical variability is reported for the extraframework
components in the cancrinite-group minerals. Two subgroups can be identified according to
the extraframework content of the can units: the cancrinite- and the davyne-subgroups,
showing Na-H2O and Ca-Cl chains, respectively. The channels are stuffed by cations, anions
and molecules.
We aimed to model the thermo-elastic behavior and the mechanisms of the
(P ,T)-induced structure evolution of cancrinite-group minerals, with special
interest on the role played by the extraframework population. The study was
restricted to the following (CO3)-rich and (SO4)-rich end-members: cancrinite
sensu stricto {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]}, vishnevite
{[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24]}, balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]}
and davyne {[(Na,Ca,K)6((SO4),Cl)][Ca2Cl2][Al6Si6O24]}. Their high-P and low-T
(T < 293 K) behavior was investigated by means of in-situ single-crystal X-ray diffraction,
using diamond-anvil cells and (N2)-cryosystems, respectively. The high-T behavior of
cancrinite has also been studied by means of in-situ single-crystal X-ray diffraction with a
resistive heater.
Cancrinite minerals share a similar volume compressibility and thermal expansivity at
ambient conditions (cancrinite has KV 0 = 45(2) GPa and αV,293K = 4.88(8)-
10-5 K-1;
vishnevite has KV 0 = 49(2) GPa; balliranoite has KV 0 = 48(3) GPa and αV,293K =
4.6(4)-
10-5 K-1; davyne has KV 0 = 46.5(11) GPa and αV,293K = 4.2(4)-
10-5 K-1).
However, these minerals show different thermo-elastic anisotropy schemes, more
pronounced in the cancrinite-subgroup minerals. This behavior is governed by different
deformation mechanisms of the crystal structure, which likely reflect the different
coordination environments of the cage-cations between the minerals of the cancrinite- and
davyne-subgroups (i.e. Na+ and Ca2+, respectively). In addition, a P -induced
re-organization of the extraframework population is observed, in vishnevite, at
P ≥ 3.5 GPa, suggesting that the channel-constituents can also affect the elastic
and structural behavior and the phase stability of these minerals at non-ambient
conditions.
Besides common features likely ascribable to the [CAN]-topology, the nature of the
extraframework population appears to control significantly the (P ,T)-induced structure
evolution and thermo-elastic behavior of the cancrinite-group compounds.
PL, GDG and MM acknowledge the Italian Ministry of Education, MIUR-Project:
“Futuro in Ricerca 2012 - ImPACT- RBFR12CLQD”.
MA acknowledges the ERC starting grant N. 307322 to FN. |
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