### Abstract

The heat capacity of synthetic andradite garnet (Ca_{3}Fe_{2}Si_{3}O_{12}) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K C^{o}_{p,m} and S^{o}_{m} are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in C^{o}_{p,m} with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe^{3+} ions. The Gibbs free energy of formation, Δ_{f}G^{o}_{m} (298.15 K) of andradite is -5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained Δ_{f}H^{o}_{m} (298.15 K) = - 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation C^{o}_{p,m} = 809.24 - 7.025 × 10-2T- 7.403 × 10^{3}T-0.5 - 6.789 × 10^{5}T-2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi_{2}O_{6}) for which we obtained Δ_{f}G^{o}_{m} (298.15 K) = -2674.3 ± 5.8 kJ/mol.

Original language | English (US) |
---|---|

Pages (from-to) | 2219-2224 |

Number of pages | 6 |

Journal | Geochimica et Cosmochimica Acta |

Volume | 51 |

Issue number | 8 |

DOIs | |

State | Published - 1987 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Geochemistry and Petrology

### Cite this

_{3}Fe

_{2}Si

_{3}O

_{12}, between 10 and 1000 K and revised values for Δ

_{f}G

^{o}

_{m}(298.15 K) of hedenbergite and wollastonite.

*Geochimica et Cosmochimica Acta*,

*51*(8), 2219-2224. https://doi.org/10.1016/0016-7037(87)90271-7

**Heat capacity and thermodynamic properties of andradite garnet, Ca _{3}Fe_{2}Si_{3}O_{12}, between 10 and 1000 K and revised values for Δ_{f}G^{o}_{m} (298.15 K) of hedenbergite and wollastonite.** / Robie, Richard A.; Bin, Zhao; Hemingway, Bruce S.; Barton, Mark D.

Research output: Contribution to journal › Article

_{3}Fe

_{2}Si

_{3}O

_{12}, between 10 and 1000 K and revised values for Δ

_{f}G

^{o}

_{m}(298.15 K) of hedenbergite and wollastonite',

*Geochimica et Cosmochimica Acta*, vol. 51, no. 8, pp. 2219-2224. https://doi.org/10.1016/0016-7037(87)90271-7

_{3}Fe

_{2}Si

_{3}O

_{12}, between 10 and 1000 K and revised values for Δ

_{f}G

^{o}

_{m}(298.15 K) of hedenbergite and wollastonite. Geochimica et Cosmochimica Acta. 1987;51(8):2219-2224. https://doi.org/10.1016/0016-7037(87)90271-7

}

TY - JOUR

T1 - Heat capacity and thermodynamic properties of andradite garnet, Ca3Fe2Si3O12, between 10 and 1000 K and revised values for ΔfGom (298.15 K) of hedenbergite and wollastonite

AU - Robie, Richard A.

AU - Bin, Zhao

AU - Hemingway, Bruce S.

AU - Barton, Mark D

PY - 1987

Y1 - 1987

N2 - The heat capacity of synthetic andradite garnet (Ca3Fe2Si3O12) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K Cop,m and Som are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in Cop,m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe3+ ions. The Gibbs free energy of formation, ΔfGom (298.15 K) of andradite is -5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained ΔfHom (298.15 K) = - 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation Cop,m = 809.24 - 7.025 × 10-2T- 7.403 × 103T-0.5 - 6.789 × 105T-2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi2O6) for which we obtained ΔfGom (298.15 K) = -2674.3 ± 5.8 kJ/mol.

AB - The heat capacity of synthetic andradite garnet (Ca3Fe2Si3O12) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K Cop,m and Som are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in Cop,m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe3+ ions. The Gibbs free energy of formation, ΔfGom (298.15 K) of andradite is -5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained ΔfHom (298.15 K) = - 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation Cop,m = 809.24 - 7.025 × 10-2T- 7.403 × 103T-0.5 - 6.789 × 105T-2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi2O6) for which we obtained ΔfGom (298.15 K) = -2674.3 ± 5.8 kJ/mol.

UR - http://www.scopus.com/inward/record.url?scp=0023486523&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0023486523&partnerID=8YFLogxK

U2 - 10.1016/0016-7037(87)90271-7

DO - 10.1016/0016-7037(87)90271-7

M3 - Article

AN - SCOPUS:0023486523

VL - 51

SP - 2219

EP - 2224

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

IS - 8

ER -