Abstract
Pyroxenes are considered as ideal solid solutions of some real components (e.g. diopside or orthoenstatite) and some fictive or hypothetical components (e.g. orthodiopside or orthohedenbergite). Using the reversed experimental data in the CaO-MgO-SiO2 system, the Gibbs free energy of formation of fictive orthodiopside and of fictive clinoenstatite have been determined in the temperature range of 1,000 to 1,600 °K. The data on free energies of components in the binary system can be used to extend the fictive component model to the ternary CaSiO3-MgSiO3-FeSiO3 system. Using published phase diagrams on the pyroxene quadrilateral, Gibbs free energy of formation of fictive orthohedenbergite has been calculated. Application of the ideally mixing fictive component model to computation of phase equilibria leads to the determination of compositions of coexisting Fe-Mg-Ca pyroxenes at different temperatures.
Similar content being viewed by others
Abbreviations
- G 0f :
-
Gibbs free energy of formation from the elements at 1 bar and temperature
- G Ex :
-
excess free energy of mixing in a solution
- G :
-
molar Gibbs free energy
- R :
-
gas constant
- H :
-
enthalpy
- S :
-
entropy
- T :
-
absolute temperature
- P :
-
pressure
- KJ/M:
-
kilojoules per mole
- j:
-
joules
- Opx:
-
orthopyroxene
- Cpx:
-
clinopyroxene
- H:
-
hedenbergite
- D:
-
diopside
- E:
-
enstatite
- F:
-
ferrosilite
- X :
-
mole fraction
- K :
-
equilibrium constant
References
Atkins FB (1969) Pyroxenes of the Bushveld intrusion, South Afric. J Petrol 10:222–249
Brown GM (1957) Pyroxenes from the early and middle stages of fractionation of the Skaergaard intrusion, East Greenland. Mineral Mag 31:511–543
Erikkson G (1976) Quantitative equilibrium calculations in multiphase systems at high temperatures with special reference to the roasting of chalcopyrite (CuFeS2). Akademisk Avhandling, Umea University, Sweden
Eriksson G, Rosen E (1973) Thermodynamic studies of high temperature equilibria. Chemica Scripta 4:193–194
Grossman L (1972) Condensation in the primitive solar nebula. Geochim Cosmochim Acta 36:109–128
Harvie CE, Weare JH (1980) The prediction of mineral solubilities in natural waters. The Na-K-Mg-Ca-Cl-SO4-H2O system from zero to high concentration at 25° C. Geochim Cosmochim Acta 44:981–997
Helgeson HC, Delany JM, Nesbitt H, Bird DK (1978) Summary and critique of the thermodynamic properties of rock-forming minerals. Am J Sci 278-A:1–250
Holland TJB, Navrotsky A, Newton RC (1979) Thermodynamic parameters of CaMgSi2O6-Mg2Si2O6 pyroxenes based on regular solution and cooperative disordering models. Contrib Mineral Petrol 69:337–344
Howie RA (1955) The geochemistry of the charnockite series of Madras, India. Trans R Soc Edinburgh 62:725–768
Howie RA (1958) African charnockites and related rocks. Service Geol Congo Belge Bull 8:1–14
Leelanandam C (1967) Chemical study of pyroxenes from the charnockitic rocks of Kondapalli (Andhra Pradesh), India. Mineral Mag 36:153–179
Lindsley DH, Dixon S (1976) Diopside-enstatite equilibria at 850° C to 1,400° C, 5 to 35 kb. Am J Sci 276a:295–324
Lindsley DH, Grover JE, Davidson PM (1981) The thermodynamics of the Mg2Si2O6-CaMgSi2O6 join: A review and a new model. In: Newton, Navrotsky and Wood (eds) Advances in physical geochemistry, Vol 1. Springer-Verlag, NY
Lindsley DH (1980) Phase equilibria of pyroxenes at pressures 1 atmosphere. In: CT Prewitt (ed) Reviews in mineralogy, Vol 7. Mineral Soc Am, pp 289–308
Mori T, Green DH (1975) Pyroxenes in the system Mg2Si2O6-CaMg-Si2O6 at high pressure. Earth Planet Sci Lett 26:277–286
Nehru CE, Wyllie PJ (1974) Electron-microprobe measurement of pyroxenes coexisting with H2O-undersaturated liquid in the join CaMgSi2O6-Mg2Si2O6 at 30 kbars with application to geothermometry. Contrib Mineral Petrol 48:221–228
Saxena SK (1973) Thermodynamics of rock-forming crystalline solutions. Springer-Verlag, NY
Saxena SK (1981) The MgO-Al2O3-SiO2 system: Free energy of pyrope and Al2O3-enstatite. Geochim Cosmochim Acta 45:821–825 (1981)
Warner RD, Luth WC (1974) The diopside-clinoenstatite two phase region in the system CaMgSi2O6-Mg2Si2O6. Am Mineral 59:98–109
Wood BJ, Banno S (1973) Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems. Contrib Mineral Petrol 42:109–124
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Saxena, S.K. Fictive component model of pyroxenes and multicomponent phase equilibria. Contr. Mineral. and Petrol. 78, 345–351 (1982). https://doi.org/10.1007/BF00398930
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00398930