The elastic constants of single-crystal orthopyroxene

The elastic constants of a very small orthopyroxene gem (1.9 grams) of the bronzite variety (density 3.335 g/cc) was measured by the pulse superposition method. The adiabatic stiffness constants in Mb at room temperature and 1 atm pressure are: c11 = 2.299, c22 = 1.654, c33 = 2.057, c44 = 0.8306, c55 = 0.7637, c66 = 0.7853, c23 = 0.496, c31 = 0.573, and c12 = 0.701. Using the Voigt-Reuss-Hill average, the dilational wave velocity is 7.85 km/sec, shear wave velocity is 4.76 km/sec, bulk modulus is 1.050 Mb, rigidity is 0.755 Mb, and Poisson's ratio is 0.21. In contrast with the properties of clinopyroxenes, the a axis in this crystal is elastically the most stiff direction, showing the maximum dilational velocity and minimum linear compressibility. The maximum velocity anisotropy of dilational waves is 126 km/sec, or 17%, which is comparable to 18% for olivine.