An X-ray diffraction and Raman spectroscopic study of the high-pressure behavior of gaspéite (Ni0.73Mg0.27CO3)

Here, we present new measurements of the phase stability and lattice compressibility of gaspéite (NiCO3) to 50 GPa. Our study is motivated by our interest in understanding high-pressure carbonate behavior. While carbonates have been extensively studied under high-pressure and -temperature conditions, they exhibit different behaviors. We have studied the high-pressure behavior of gaspéite using diamond anvil cells, Raman spectroscopy, and X-ray diffraction. Our experimental data show that gaspéite maintains the calcite structure up to 50 GPa, reverts to its zero-pressure volume on decompression with little hysteresis, and can be fit by a 3rd-order Birch–Murnaghan equation of state. We calculate a bulk modulus (K0T) of 136(4) GPa and a K′ value of 4.6(3). Additionally, we have determined the isothermal Grüneisen parameter for each of the traced Raman modes. These results contribute to growing experimental evidence that suggests some carbonates can be stable at lower mantle conditions. Ultimately, information in this dataset may facilitate predictions of mixing energetics amongst the calcite-structured carbonates, and therefore help determine the role of carbonates in the transition metal geochemistry of the deep Earth.