Elasticity of single-crystal calcite and rhodochrosite by Brillouin spectroscopy

The single-crystal elastic moduli of natural samples of both calcite (CaCO3 ) and rhodochrosite (MnCO3) have been measured by Brillouin spectroscopy un der ambient condition. Based on the trigonal unit cell, the elastic constan ts C-11, C-33, C-44, C-12, C-13, and C-14 are 149.4(7), 85.2(18), 34.1(5), 57.9(11), 53.5(9), -20.0(2), and 223.9(15), 132.6(41), 44.5(9), 93.4(21), 7 6.0(23), -17.3(6) GPa for CaCO3 and MnCO3, respectively. Our data for calci te are in good agreement with earlier data obtained by ultrasonic experimen ts. The off-diagonal elastic constants (C-12, C-13, and C-14) for rhodochro site have systematically larger values than the trend defined by other isos tructural carbonates, in all of which the divalent cations are alkaline-ear th metals. This is a distinctive signature of transition-metal-bearing oxid es, which is present in silicates and simple oxides as well.