EQUATION OF STATE, ELASTICITY, AND SHEAR STRENGTH OF PYRITE UNDER HIGH PRESSURE

Abstract

Physical properties including the equation of state, elasticity, and shear strength of pyrite have been measured by a series of X-ray diffraction in diamond-anvil cells at pressures up to 50 GPa. A Birch-Murnaghan equation of state fit to the quasihydrostatic pressure-volume data obtained from laboratory X-ray source/film techniques yields a quasihydrostatic bulk modulus K0T=133.5 (±5.2) GPa and bulk modulus first pressure derivative K′0T=5.73 (±0.58). The apparent equation of state is found to be strongly dependent on the stress conditions in the sample. The stress dependency of the high-pressure properties is examined with anisotropic elasticity theory from subsequent measurements of energy-dispersive radial diffraction experiments in the diamond-anvil cell. The calculated values of K0T depend largely upon the angle ψ between the diffracting plane normal and the maximum stress axis. The uniaxial stress component in the sample,t=σ3−σ1, varies with pressure as t=-3.11+0.43P between 10 and 30 GPa. The pressure derivatives of the elastic moduli dC11/dP=5.76 (±0.15), dC12/dP=1.41 (±0.11) and dC44/dP=1.92 (±0.06) are obtained from the diffraction data assuming previously reported zero-pressure ultrasonic data (C11=382 GPa, C12=31 GPa, and C44=109 GPa).