Quasi-hydrostatic compression of ruby to 500 Kbar

Measurements of the cell parameters of ruby to 500 Kbar under quasi-hydrostatic conditions in a diamond-anvil cell show a practically isotropic compression, the ratio c/a of the hexagonal cell parameters remaining constant. These results are consistent with previous single-crystal measurements below 100 Kbar as well as with ultrasonic elastic-constant measurements. There is no evidence for significant differences between the bulk moduli of ruby and corundum, and a review of compression and ultrasonic data yield Ko = 2.53±0.01 Mbar and Ko = 5.0 ± 0.4. Good agreement with the experimental values is found for compressions calculated from empirically or theoretically determined elastic properties.