We determined elastic constants of a single-crystal chromian spinel at temperatures from −15 to 45 °C through the Rectangular Parallelepiped Resonance method. The sample is a natural chromian spinel, which was separated from a mantle xenolith. Elastic constants at an ambient temperature (T = 24.0 °C) are C11 = 264.8(1.7) GPa, C12 = 154.5(1.8) GPa and C44 = 142.6(0.3) GPa. All the elastic constants decrease linearly with increasing temperature. The temperature derivatives are dC11/dT = −0.049(2) GPa/°K, dC12/dT = −0.019(1) GPa/°K and dC44/dT = −0.020(1) GPa/°K. As an implication of the elastic constants, we applied them to the correction of a fluid inclusion geobarometry, which utilizes residual pressure of fluid inclusion as a depth scale. Before entrainment by a magma, the fluid inclusions must have the identical fluid density in constituent minerals of a xenolith. It has been, however, pointed out that fluid density of fluid inclusions significantly varies with host mineral species. The present study elucidates that elastic constants and thermal expansion coefficients cannot explain the difference in fluid density among mineral species. The density difference would reflect the difference in the degree of plastic deformation in the minerals.
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