An X-Ray Diffraction Study of the High Pressure Behavior of Gaspéite (NiCO3)
Abstract
Our study of the behavior of gaspéite (NiCO3) at high pressures is motivated by our interest in the high-pressure behavior of carbonates as well as the high-pressure behavior of transition metals in a variety of their crystal environments. Zhang and Reeder (1999) measured phase stability and compressibility of a variety of calcite-structured carbonates up to 8 GPa. Here we present new measurements of the phase stability and lattice compressibility of gaspéite to 39 GPa.
Three separate high-pressure powder x-ray diffraction experiments were conducted on natural samples of gaspéite (NiCO3) up to 39 GPa. The sample composition determined by SEM is (Ni0.73,Mg0.27)CO3. The room pressure volumes inferred from the equation of state measurements indicate a compositional range of Ni from 0.7-0.76, when interpreted in terms of linear mixing between Ni and Mg end-member data from Zhang and Reeder (1999). Samples were loaded into a symmetric-type diamond anvil cell with ruby to determine pressure and gas-loaded with Ne which served as a pressure medium. XRD measurements runs 1 and 2 were made at beamline 13-ID-D at the Advanced Photon Source in Chicago, IL and run 3 at beamline 12.2.2 at the Advanced Light Source in Berkeley, CA. Diffraction patterns were collected at each pressure step. Gaspéite maintains its calcite structure up to 40 GPa, and reverts to its room-pressure volume on decompression with some hysteresis. A Birch-Murnaghan equation of state was fit to the three data sets yielding KOT = 110(10) GPa and K' = 10(1) for run 1, KOT = 122(7) GPa and K' = 8(1) for run 2, and KOT = 112(11) GPa and K'=10(1) for run 3. All three runs are characterized by an unusually high K', indicating a strong higher-order component to the fit. A comparison of the c/a ratios of the calcite-structured carbonates shows similar pressure-dependencies, except for gaspéite at the extreme pressures of this study which show a marked c/a decrease. We present these results in the context of the transition metal calcite-structured carbonates, showing systematics in the compressibility and c/a ratio as a function of volume. These measurements facilitate predictions of mixing energetics amongst the calcite-structured carbonates, as well as first-row divalent transition metal mineral species.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR41B0060S
- Keywords:
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- 1042 Mineral and crystal chemistry;
- GEOCHEMISTRY;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3999 General or miscellaneous;
- MINERAL PHYSICS;
- 3620 Mineral and crystal chemistry;
- MINERALOGY AND PETROLOGY;
- 3672 Planetary mineralogy and petrology;
- MINERALOGY AND PETROLOGY;
- 5430 Interiors;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 7208 Mantle;
- SEISMOLOGY