Heat capacity and thermodynamic properties of andradite garnet, Ca/sub 3/Fe/sub 2/Si/sub 3/O/sub 12/, between 10 and 1000 K and revised values for. delta. /sub f/G/sub m//sup 0/ (298. 15 K) of hedenbergite and wollastonite

Journal Article · Sat Aug 01 00:00:00 EDT 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90271-7· OSTI ID:5099802

Robie, R A; Bin, Z; Hemingway, B S; Barton, M D

The heat capacity of synthetic andradite garnet (Ca/sub 3/Fe/sub 2/Si/sub 3/O/sub 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/sub p,m//sup 0/ and S/sub m//sup 0/ are 351.9 +- 0.7 and 316.4 +- 2.0 J(mol x K), respectively. Andradite has a lambda-peak in C/sub p,m//sup 0/ with a maximum at 11.7 +- 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe/sup 3 +/ ions. The Gibbs free energy of formation, ..delta../sub f/G/sub m//sup 0/ (298.15 K) of andradite is -5414.8 +- 5.5 kJmol, and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at approx. 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained ..delta../sub f/H/sub m//sup 0/ (298.15 K) = -1634.5 +- 1.8 kJmol for wollastonite. The authors have also used their thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi/sub 2/O/sub 6/) for which we obtained ..delta../sub f/G/sub m//sup 0/ (298.15 K) = -2674.3 +- 5.8 kJmol.

• Research Organization: Geological Survey, Reston, VA (USA)
• OSTI ID: 5099802
• Journal Information: Geochim. Cosmochim. Acta; (United States), Vol. 51:8
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GARNETS
SPECIFIC HEAT
THERMODYNAMIC PROPERTIES
HEDENBERGITE
SILICATE MINERALS
CALORIMETRY
FREE ENTHALPY
SILICON OXIDES
SYNTHETIC MATERIALS
TEMPERATURE EFFECTS
CHALCOGENIDES
ENERGY
MATERIALS
MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PYROXENES
SILICATES
SILICON COMPOUNDS
580400* - Geochemistry- (-1989)