***Thermodynamic*** properties of calcium-, strontium-, and barium feldspars based on ***calorimetric*** data

Abstract

Values of the std. ***enthalpy*** of formation of CaAl2Si2O8 (synthetic anorthite), SrAl2Si2O8, and BaAl2Si2O8 (synthetic celsian) were detd. based on high-temp microcalorimetry by the Calvet method of dissoln. in 2PbO.cntdot.B2O3 melt. The ***enthalpy*** of soln. (.DELTA.H.degree.973) and ***heat*** of ***formation*** (.DELTA.fH.degree.298.15) values obtained were: anorthite (64.45 .+-. 0.79, -4221.5 .+-. 4.6 kJ/mol, resp.), Sr feldspar (86.96 .+-. 2.2, -4248.0 .+-. 4.7 kJ/mol, resp.), and celsian (109.16 .+-. 1.05, -4244.3 .+-. 1.2 kJ/mol, resp.).