Publication Date:
2020-11-17
Description:
high-pressure behavior of three synthetic
amphiboles crystallized with space group P21/m at room
conditions in the system Li2O–Na2O–MgO–SiO2–H2O
has been studied by in situ synchrotron infrared absorption
spectroscopy. The amphiboles have compositions
ANa B(NaxLi1 ¡ xMg1) CMg5 Si8 O22(OH)2 with x = 0.6, 0.2
and 0.0, respectively. The high-P experiments up to 32 GPa
were carried out on the U2A beamline at Brookhaven
National Laboratory (NY, USA) using a diamond anvil cell
under non-hydrostatic or quasi-hydrostatic conditions. The
two most intense absorption bands in the OH-stretching
infrared spectra can be assigned to two non-equivalent O–H
dipoles in the P21/m structure, bonded to the same local
environment M1M3Mg3–OH–ANa, and pointing toward two
diVerently kinked tetrahedral rings. In all samples these
bands progressively merge to give a unique symmetrical
absorption with increasing pressure, suggesting a change in
symmetry from P21/m to C2/m. The pressure at which the
transition occurs appears to be linearly correlated to the
aggregate B-site dimension. The infrared spectra collected
for amphibole B(Na0.2Li0.8Mg1) in the frequency range 50
to 1,400 cm¡1 also show a series of changes with increasing
pressure. The data reported here support the inference of
Iezzi et al. (Am Miner 91:479–482, 2006a) regarding a new
high-pressure C2/m amphibole polymorph characterized by
two equivalent and kinked double-chains, stable at very
high-pressure.
Description:
Published
Description:
343–354
Description:
2IT. Laboratori analitici e sperimentali
Description:
JCR Journal
Description:
reserved
Keywords:
High-pressure
;
B-site dimension
;
04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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