On the elastic behaviour of zeolite paulingite: a synchrotron powder diffraction study

R. Skála^1,2, G. D. Gatta³, Y. Lee⁴

¹Inst. of Geology AV ČR, Rozvojová 269, 16500 Praha 6, Czech Republic

²ÚGMNZ, Faculty of Science, Charles University, Albertov 6, 12843 Praha 2, Czech Republic

³Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli 23, I-20133 Milano, Italy

⁴ Physics Dept., Brookhaven National Laboratory, Upton, NY 11973–5000, USA

skala@gli.cas.cz

The high-pressure (HP) elastic behaviour of a zeolite paulingite found in vugs in olivine nephelinite of the Vinařická hora Hill Tertiary volcano near Kladno (Czech Republic) was studied by means of in situ synchrotron X-ray powder diffraction. The diffraction experiments were performed using a diamond anvil cell (DAC) at the X7A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. A gas-proportional position-sensitive detector was stepped in 0.25 °2θ intervals over the angular range of 3–35 °2θ with counting times of 90 - 150 s per step. The wavelength of the incident beam (0.60046 Å), PSD zero channel, and PSD degrees per channel were determined from a CeO₂ standard (SRM 674). A powdered sample of pauligite was placed in the gasket hole of the DAC together with some ruby chips. The pressure at the sample was measured by detecting the shift in the R1 emission line of the ruby chips with precision ± 0.1 GPa. Two sets of experiments were carried out with two different pressure-transmitting media: a nominally penetrating methanol : ethanol : water (16:3:1) mixture and a nominally non-penetrating silicon oil. The maximum pressures attained in the experiments were 5.12 GPa in the case of alcohol : water mixture and 2.53 GPa in the case of silicon oil. The chemical composition of the studied sample, K_4.87Na_0.37Ca_3.20Ba_0.23Mg_0.04Sr_0.03Fe_0.05Al_11.17Si_30.52O₈₄ . 30 H₂O, has been determined by an electron microprobe analyser CAMECA SX-100. Unit cell parameters were determined by LeBail whole powder pattern fitting implemented in the FullProf suite. Axial and volume bulk moduli have been calculated using a truncated second-order Birch–Murnaghan equation-of-state using program EOSFIT. No phase transition or sample decomposition have been observed up to the maximum recorded pressures. The bulk moduli refined from the data collected in nominally penetrating medium were excessively high pointing out that paulingite is over-hydrated under the conditions of the experiment. The refined elastic parameters for the experiment with nominally non-penetrating medium are: V₀ = 43794(185) ų, K_T0 = 18(1) GPa.