A single-crystal of Ca0.2Sr0.8Al2Si2O8 having I-1 symmetry at room conditions has been loaded into a diamond anvil cell together with a quartz single-crystal as internal pressure standard. Unit-cell parameters were measured as a function of pressure up to 7.7 GPa. At pressure above 4 GPa a first-order transition from triclinic to monoclinic symmetry is observed, indicated by the change in a and g unit-cell angles. Careful cycling above and below the transition has shown the presence of hysteresis between 4.0 and 4.3 GPa. This transition is likely to be the I-1 to I2/c phase transformation observed for the same sample with increasing temperature, suggesting that also for the triclinic CaSr-feldspars, as in the case of anorthite, the high-pressure low-temperature and the high-temperature low-pressure phase boundaries have different Clapeyron slopes. EoS parameters for the triclinic phase calculated up to 4.1 GPa using a Birch-Murnaghan equation of state are V0=1393.97(5) Å K0=88.7(7) GPa and K'=1.5(2). Evidence of a further first-order phase transformation from monoclinic to monoclinic symmetry have been found at pressure above 7 GPa with a volume change of ~ 1.5%.

High-pressure behavior of Ca0.2Sr0.8Al2Si2O8 feldspar.

BENNA, Piera;TRIBAUDINO M.;BRUNO, Emiliano
2003

Abstract

A single-crystal of Ca0.2Sr0.8Al2Si2O8 having I-1 symmetry at room conditions has been loaded into a diamond anvil cell together with a quartz single-crystal as internal pressure standard. Unit-cell parameters were measured as a function of pressure up to 7.7 GPa. At pressure above 4 GPa a first-order transition from triclinic to monoclinic symmetry is observed, indicated by the change in a and g unit-cell angles. Careful cycling above and below the transition has shown the presence of hysteresis between 4.0 and 4.3 GPa. This transition is likely to be the I-1 to I2/c phase transformation observed for the same sample with increasing temperature, suggesting that also for the triclinic CaSr-feldspars, as in the case of anorthite, the high-pressure low-temperature and the high-temperature low-pressure phase boundaries have different Clapeyron slopes. EoS parameters for the triclinic phase calculated up to 4.1 GPa using a Birch-Murnaghan equation of state are V0=1393.97(5) Å K0=88.7(7) GPa and K'=1.5(2). Evidence of a further first-order phase transformation from monoclinic to monoclinic symmetry have been found at pressure above 7 GPa with a volume change of ~ 1.5%.
2003 Seattle Annual Meeting
Seattle (Washington)
2-5 novembre, 2003.
GSA Seattle (Washington)
The Geological Society of America
35
219
219
High-pressure; feldspar
BOFFA BALLARAN T.; NESTOLA F.; BENNA P.; TRIBAUDINO M.; BRUNO E.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/111307
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