TY - JOUR
T1 - The enthalpy of formation and internally consistent thermodynamic data of Mg-staurolite
AU - Grevel, Klaus D.
AU - Navrotsky, Alexandra
AU - Fockenberg, Thomas
AU - Majzlan, Juraj
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2002
Y1 - 2002
N2 - The enthalpies of drop solution in lead borate (2PbO·B2O3) of four Mg-staurolite samples, synthesized at 720°C and pressures between 2 and 5 GPa, were measured by high-temperature oxidemelt calorimetry at 702°C. Staurolite compositions, determined by electron microprobe analysis. Karl-Fischer titration, and thermogravimetry, are: Mg3.71A118.60O44.31(OH)3.69. Mg3.58A118.05Si7.43O43.01(OH) 4.99. The enthalpy of drop solution of the bulk samples (as well as the calculated values for the enthalpy of formation from the elements of Mg-staurolite) are strongly correlated to the H content of the samples. The enthalpy of formation from the elements is best described by the linear relation ΔfHo298 (Mg-staurolite) = (-25357.58 + 87.35 N) kJ/mol. where N = number of H atoms per formula unit in Mg-staurolite. The enthalpy of drop solution of two partially dehydrated Mg-staurolite samples is in a good agreement with the linear relation. Phase-equilibrium data for Mg-staurolite (Fockenberg 1998) were recalculated using the stoichiometric formula Mg3.5Al18Si7.75O44(OH)4 . Based on these mineral equilibria and the internally consistent data set of Berman (1988), a mathematical programming analysis of the thermodynamic data of Mg-staurolite gave ΔfHo298 [Mg3.5Al18Si7.75O44(OH)4 ] = -25005.14 kJ/mol, and So298 [Mg3.5Al18Si7.75O44(OH)4 ] = 937.94 J/(K·mol). Thus, for the first time, reliable thermodynamic data for Mg-staurolite, based on experimental constraints, are provided.
AB - The enthalpies of drop solution in lead borate (2PbO·B2O3) of four Mg-staurolite samples, synthesized at 720°C and pressures between 2 and 5 GPa, were measured by high-temperature oxidemelt calorimetry at 702°C. Staurolite compositions, determined by electron microprobe analysis. Karl-Fischer titration, and thermogravimetry, are: Mg3.71A118.60O44.31(OH)3.69. Mg3.58A118.05Si7.43O43.01(OH) 4.99. The enthalpy of drop solution of the bulk samples (as well as the calculated values for the enthalpy of formation from the elements of Mg-staurolite) are strongly correlated to the H content of the samples. The enthalpy of formation from the elements is best described by the linear relation ΔfHo298 (Mg-staurolite) = (-25357.58 + 87.35 N) kJ/mol. where N = number of H atoms per formula unit in Mg-staurolite. The enthalpy of drop solution of two partially dehydrated Mg-staurolite samples is in a good agreement with the linear relation. Phase-equilibrium data for Mg-staurolite (Fockenberg 1998) were recalculated using the stoichiometric formula Mg3.5Al18Si7.75O44(OH)4 . Based on these mineral equilibria and the internally consistent data set of Berman (1988), a mathematical programming analysis of the thermodynamic data of Mg-staurolite gave ΔfHo298 [Mg3.5Al18Si7.75O44(OH)4 ] = -25005.14 kJ/mol, and So298 [Mg3.5Al18Si7.75O44(OH)4 ] = 937.94 J/(K·mol). Thus, for the first time, reliable thermodynamic data for Mg-staurolite, based on experimental constraints, are provided.
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U2 - 10.2138/am-2002-0403
DO - 10.2138/am-2002-0403
M3 - Article
AN - SCOPUS:0036098826
SN - 0003-004X
VL - 87
SP - 397
EP - 404
JO - American Mineralogist
JF - American Mineralogist
IS - 4
ER -