Heat capacities and thermodynamic properties of braunite (Mn 7 SiO 12 ) and rhodonite (MnSiO 3 )

Other| June 01, 1995 Heat capacities and thermodynamic properties of braunite (Mn7SiO12) and rhodonite (MnSiO3) Richard A. Robie; Richard A. Robie U. S. Geological Survey, Reston, VA, United States Search for other works by this author on: GSW Google Scholar J. Stephen Huebner; J. Stephen Huebner Search for other works by this author on: GSW Google Scholar Bruce S. Hemingway Bruce S. Hemingway Search for other works by this author on: GSW Google Scholar American Mineralogist (1995) 80 (5-6): 560–575. https://doi.org/10.2138/am-1995-5-615 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Richard A. Robie, J. Stephen Huebner, Bruce S. Hemingway; Heat capacities and thermodynamic properties of braunite (Mn7SiO12) and rhodonite (MnSiO3). American Mineralogist 1995;; 80 (5-6): 560–575. doi: https://doi.org/10.2138/am-1995-5-615 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The heat capacities, CP0⁠, of synthetic rhodonite (MnSiO3) and braunite (Mn7SiO12) have been measured by adiabatic calorimetry from 6 to ~350 K. The heat capacity of braunite was also measured to ~900 K by differential scanning calorimetry. Braunite exhibits a λ-peak (paramagnetic to antiferromagnetic transition) in CP0 in the temperature region 93.4–94.2 K. Rhodonite did not show the expected peak in CP0 characteristic of the cooperative ordering of the Mn2+ spins at temperatures above 6 K.At 298.15 K the standard molar entropy of rhodonite is 100.5 ± 1.0 and that of braunite is 416.4 ± 0.8 J/(mol·K). For rhodonite, ΔfH0(MnSiO3, 298.15 K) is −1321.6 ± 2.0 kJ/mol. For braunite, the value for ΔfH0(Mn7SiO12, 298.15 K), −4260 ± 3.0 kJ/mol, was obtained by considering both calorimetric and phase-equilibrium data. Our heat capacity and entropy values were combined with existing thermodynamic data for MnCO3, CO2, SiO2, MnO, and Mn3O4 in a "third-law" analysis of several phase equilibrium studies and yielded ΔfG0(MnSiO3 298.15 K) = −1244.7 ± 2.0 kJ/mol and ΔfG0(Mn7SiO12, 298.15 K) = −3944.7 ± 3.8 kJ/mol from the elements.A revised petrogenetic grid for the system Mn-Si-O-C at 2000 bars is presented and is consistent with both thermochemical values and occurrence of natural assemblages. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.