A High Pressure XRD Study of Structural Changes in Anglesite
Abstract
Anglesite (PbSO4) is isostructural with barite, an important sulfur-bearing constituent in the crust. Thus, anglesite's mechanisms for deforming under pressure yield insights into deep Earth sulfate storage and cycling. Previous spectroscopic studies have suggested anglesite undergoes structural changes at about 14, 21, and 35 GPa (Lee et. al., 2013, Sawchuk et. al., in preparation). However, a recent X-ray diffraction study shows no evidence of a phase transition up to 21.6 GPa (Li et. al., 2018). Here we report new X-ray diffraction measurements detailing the high-pressure structural evolution of anglesite (PbSO4) to 45 GPa. Powder X-ray diffraction data were obtained at beamline 12.2.2 at the Advanced Light Source (ALS). Natural samples of anglesite were ground into a powder, loaded into a diamond anvil cell with ruby, and a Ne pressure medium. In the first experiment the sample was pressurized in 5 GPa steps to 30 GPa, after which the sample was laser heated and quenched. In the second experiment the sample was pressurized to 45 GPa in 2 GPa steps and decompressed in steps of 5-10 GPa. Diffraction patterns were collected and indexed as anglesite.
A fit of the volume versus pressure data to the Birch-Murnaghan equation of state yields an isothermal bulk modulus of KOT=58 ±2 GPa and a pressure derivative of K'=5.2 ±0.3. While all of the diffraction patterns on compression and decompression can be identified as anglesite we observe two changes at 21 and 40 GPa. Above 21 GPa two new diffraction peaks appear without any corresponding changes in the lattice parameters compressibility. This may indicate a pressure induced change in symmetry. Around 40 GPa we observe discontinuous shifts in the compressibility of the lattice parameters, but without the appearance of new diffraction peaks suggesting symmetry-preserving structural distortion occurs. These changes are consistent with those observed in infrared and Raman spectroscopic studies. The combination vibrational spectroscopy and X-ray diffraction helps elucidate the multiple mechanisms of compressibility of volatile-bearing minerals.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR23B0089S
- Keywords:
-
- 1038 Mantle processes;
- GEOCHEMISTRYDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 3630 Experimental mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 5199 General or miscellaneous;
- PHYSICAL PROPERTIES OF ROCKS