Elasticity of superhydrous B

The adiabatic single-crystal elastic moduli of superhydrous B, Mg₁₀Si₃O₁₄(OH)₄, have been measured at ambient conditions using Brillouin spectroscopy. This material is the first hydrous phase found to be stable at the extreme conditions of 20 GPa and 1400 °C. The single-crystal moduli, in GPa, are: C ₁₁=280.0±1.5, C ₂₂=307.4±1.6, C ₃₃=293.4±1.4, C ₄₄=90.0±1.1, C ₅₅=99.2±0.8, C ₆₆=89.6±0.6, C ₁₂=66.1±2.2, C ₁₃=105.6±2.6, C ₂₃=81.8±2.6. With aggregate elastic properties of K _VRH =154.0±4.2 and μ _VRH =97.0±0.7 GPa, superhydrous B is approximately 16% suffer than forsterite and 20% softer than magnesium silicate spinel; it is also considerably more elastically isotropic than forsterite. The single-crystal moduli are compared to those of forsterite, magnesium silicate spinel and periclase, materials that are both structurally and compositionally similar to superhydrous B. The longitudinal moduli of superhydrous B and forsterite follow similar trends and appear to be dominated by the incompressibility and rotation of silicon tetrahedra. The shear and off-diagonal moduli more closely resemble those of periclase and spinel and may reflect the properties inherent to layers of magnesium octahedra.