TY - JOUR
T1 - Thermochemistry of glasses along joins of pyroxene stoichiometry in the system Ca2Si2O6-Mg2Si2O6-Al4O6
AU - Hervig, Richard
AU - Scott, Derry
AU - Navrotsky, Alexandra
N1 - Funding Information:
Acknowledgements-This work was supported by the U.S. Department of Energy (Contract DEAC02-80ERI0765) and the National Science Foundation (Grant EAR 8022223). We thank Jim Clark of the A.S.U. Chemistry Department electron microprobe facility for assisting with the analyses and M. Ozima and E. Ito for the enstatite crystals.
PY - 1985/7
Y1 - 1985/7
N2 - Enthalpies of solution in 2PbO · B2O3 at 974 K have been measured for glasses along the joins Ca2Si2O6 (Wo)-Mg2Si2O6 (En) and Mg2Si2O6-MgAl2SiO6 (MgTs). Heats of mixing are symmetric and negative for Wo-En with WH = -31.0 ± 3.6 kJ mol-. Negative heats of mixing were also found for the En-MgTs glasses (WH = -33.4 ± 3.7 kJ mol-). Enthalpies of vitrification of pyroxenes and pyroxenoids generally increase with decreasing alumina content and with decreasing basicity of the divalent cation. Heats of mixing along several glassy joins show systematic trends. When only non-tetrahedral cations mix (outside the aluminosilicate framework), small exothermic heats of mixing are seen. When both nontetrahedral and framework cations mix (on separate sublattices, presumably), the enthalpies of mixing are substantially more negative. Maximum enthalpy stabilization near compositions with Al/Si ≈ 1 is suggested.
AB - Enthalpies of solution in 2PbO · B2O3 at 974 K have been measured for glasses along the joins Ca2Si2O6 (Wo)-Mg2Si2O6 (En) and Mg2Si2O6-MgAl2SiO6 (MgTs). Heats of mixing are symmetric and negative for Wo-En with WH = -31.0 ± 3.6 kJ mol-. Negative heats of mixing were also found for the En-MgTs glasses (WH = -33.4 ± 3.7 kJ mol-). Enthalpies of vitrification of pyroxenes and pyroxenoids generally increase with decreasing alumina content and with decreasing basicity of the divalent cation. Heats of mixing along several glassy joins show systematic trends. When only non-tetrahedral cations mix (outside the aluminosilicate framework), small exothermic heats of mixing are seen. When both nontetrahedral and framework cations mix (on separate sublattices, presumably), the enthalpies of mixing are substantially more negative. Maximum enthalpy stabilization near compositions with Al/Si ≈ 1 is suggested.
UR - http://www.scopus.com/inward/record.url?scp=0022181088&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0022181088&partnerID=8YFLogxK
U2 - 10.1016/0016-7037(85)90254-6
DO - 10.1016/0016-7037(85)90254-6
M3 - Article
AN - SCOPUS:0022181088
SN - 0016-7037
VL - 49
SP - 1497
EP - 1501
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 7
ER -