## 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 |

### Bibliographical note

Funding Information:Carlo Meneghini is acknowledged for the use of the software Scan_Zero, used for integration of translational imaging-plate data, and for helpful discussions. ESRF is thanked for the allocation of beam time. GDG thanks the Italian MIUR (grant no. 2008SPZ743 ). YL thanks the support by Mid-career Researcher Program through NRF grant funded by the Ministry of Education, Science and Technology (MEST) of the Korean Government (No. 2009-0083847). Experiments at PAL were supported in part by MEST and Pohang University of Science and Technology (POSTECH). M. Welch, an anonymous reviewer and the editor M. Rieder are thanked for their suggestions.

## All Science Journal Classification (ASJC) codes

- Materials Science(all)
- Geochemistry and Petrology