Unit-cell parameters have been determined on a single crystal of pyrope mounted in a dia-mond-anvil cell at pressures from one atm to 50 kbar. From a least-squares fit of these data to a third-order Birch-Murnaghan equation of state, a value for the bulk modulus of pyrope (KT = 1.75 Mbar) and its pressure derivative (K'T = 4.5) were calculated. The bulk modulus is in good agreement with two other determinations using cubic-anvil and acoustic techniques but does not agree with another determination using single-crystal diamond-anvil techniques. It appears possible to obtain reasonable values and errors for K'T with diamond-anvil techniques at low pressures (<50 kbar), even for minerals with large values of KT, when complementary acoustic data are available.

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