## Abstract

The thermo-elastic behavior of a natural epidote [Ca_{1.925} Fe_{0.745}Al_{2.265}Ti_{0.004}Si_{3.037}O_{12}(OH)] has been investigated up to 1,200 K (at 0.0001 GPa) and 10 GPa (at 298 K) by means of in situ synchrotron powder diffraction. No phase transition has been observed within the temperature and pressure range investigated. P-V data fitted with a third-order Birch-Murnaghan equation of state (BM-EoS) give V_{0} = 458.8(1)Å^{3}, K_{T0} = 111(3) GPa, and K′ = 7.6(7). The confidence ellipse from the variance-covariance matrix of K_{T0} and K′ from the least-square procedure is strongly elongated with negative slope. The evolution of the "Eulerian finite strain" vs "normalized stress" yields Fe(0) = 114(1) GPa as intercept values, and the slope of the regression line gives K′ = 7.0(4). The evolution of the lattice parameters with pressure is slightly anisotropic. The elastic parameters calculated with a linearized BM-EoS are: a_{0} = 8.8877(7) Å, K_{T0}(a) = 117(2) GPa, and K′(a) = 3.7(4) for the a-axis; b_{0} = 5.6271(7) Å, K_{T0}(b) = 126(3) GPa, and K′(b) = 12(1) for the b-axis; and c_{0} = 10.1527(7) Å, K_{T0}(c) = 90(1) GPa, and K'(c) = 8.1(4) for the c-axis [K_{T0}(a):K_{T0}(b):K_{T0}(c) = 1.30:1.40:1]. The β angle decreases with pressure, β_{P}(°) = β_{P0} -0.0286(9)P +0.00134(9)P^{2} (P in GPa). The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α_{0} + α_{1}T^{-1/2}. The refined parameters for epidote are: α_{0} = 5.1(2) × 10^{-5} K^{-1} and α_{1} = -5.1(6) × 10^{-4} K^{1/2} for the unit-cell volume, α_{0}(a) = 1.21(7) × 10^{-5} K^{-1} and α_{1}(a) = -1.2(2) × 10^{-4} K^{1/2} for the a-axis, α_{0}(b) = 1.88(7) × 10^{-5} K^{-1} and α_{1}(b) = -1.7(2) × 10^{-4} K^{1/2} for the b-axis, and α_{0}(c) = 2.14(9) × 10^{-5} K^{-1} and α_{1}(c) = -2.0(2) × 10^{-4} K^{1/2} for the c-axis. The thermo-elastic anisotropy can be described, at a ry α_{0}(a): α_{0}(b): α_{0}(c) =1'G.D:1.55:1.77. The β angle increases continuously with T, with β_{T}(°) = β_{T0} + 2.5(1) × 10^{-4}T + 1.3(7) × 10^{-8}T^{2}. A comparison between the thermo-elastic parameters of epidote and clinozoisite is carried out.

Original language | English |
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Pages (from-to) | 419-428 |

Number of pages | 10 |

Journal | Physics and Chemistry of Minerals |

Volume | 38 |

Issue number | 6 |

DOIs | |

Publication status | Published - 2011 Jun |

## All Science Journal Classification (ASJC) codes

- Materials Science(all)
- Geochemistry and Petrology