TY - JOUR
T1 - Thermodynamics of element partitioning
T2 - (1) Systematics of transition metals in crystalline and molten silicates and (2) Defect chemistry and "the Henry's law problem"
AU - Navrotsky, Alexandra
N1 - Funding Information:
This work was supported by the National Science Foundation (Grant DMR77-18235). I thank M. Blander and J. Ganguly for critical reviews of this manuscript.
PY - 1978/6
Y1 - 1978/6
N2 - The distribution of Mg, Mn, Fe, Co and Ni among olivine, orthopyroxene, calcic clinopyroxene and liquid can be described by exchange reactions of the form: M (phase A) + Mg (phase B) = M (phase B) + Mg (phase A). The thermochemical data predict the observed partitioning within the limits of error of both sets of data when assumptions of ideal solid solution are used, except for Mn-Mg exchange. Because ΔS and ΔV for these exchange reactions are generally small, KD varies relatively little with temperature and pressure, although individual ion distribution coefficients (D values) are more sensitive to these variables and to changing liquid composition. Trace elements present at the ppm level can enter crystals in normal lattice sites, can participate in point defect equilibria and can enter various defect sites present metastably in the crystal as a result of its P,T history. Metastable defect equilibria, in which the number of sites (grain boundaries, surfaces, intergrowths, etc.) is fixed, can lead to enhanced trace element solubility in the crystal at very low concentrations and thus to apparent deviations from Henry's law.
AB - The distribution of Mg, Mn, Fe, Co and Ni among olivine, orthopyroxene, calcic clinopyroxene and liquid can be described by exchange reactions of the form: M (phase A) + Mg (phase B) = M (phase B) + Mg (phase A). The thermochemical data predict the observed partitioning within the limits of error of both sets of data when assumptions of ideal solid solution are used, except for Mn-Mg exchange. Because ΔS and ΔV for these exchange reactions are generally small, KD varies relatively little with temperature and pressure, although individual ion distribution coefficients (D values) are more sensitive to these variables and to changing liquid composition. Trace elements present at the ppm level can enter crystals in normal lattice sites, can participate in point defect equilibria and can enter various defect sites present metastably in the crystal as a result of its P,T history. Metastable defect equilibria, in which the number of sites (grain boundaries, surfaces, intergrowths, etc.) is fixed, can lead to enhanced trace element solubility in the crystal at very low concentrations and thus to apparent deviations from Henry's law.
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U2 - 10.1016/0016-7037(78)90100-X
DO - 10.1016/0016-7037(78)90100-X
M3 - Article
AN - SCOPUS:0001108939
SN - 0016-7037
VL - 42
SP - 887
EP - 902
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 6
ER -