Hostname: page-component-cd9895bd7-7cvxr Total loading time: 0 Render date: 2024-12-27T22:35:42.439Z Has data issue: false hasContentIssue false
  • English
  • Français

The alkali-feldspar solvus at 1 kilobar water-vapour pressure

Published online by Cambridge University Press:  05 July 2018

Peter Smith  and
Ian Parsons
Peter Smith
Affiliation:
Department of Geology and Mineralogy, University of Aberdeen, Aberdeen, AB9 IAS, Scotland
Ian Parsons
Affiliation:
Department of Geology and Mineralogy, University of Aberdeen, Aberdeen, AB9 IAS, Scotland
Get access Rights & Permissions [Opens in a new window]

Summary

The compositions of feldspar pairs crystallized from stoichiometric alkali feldspar gels with water at PH2O ≈ 1 kbar in runs of up to 3000 hours' duration vary with Na:K in the starting material. This is because, for most bulk compositions, rapid nucleation in the gel leads to growth of one feldspar phase outside the solvus. The composition of this initial feldspar phase can be thought of as reflecting the configuration of the liquidus-solidus curves in the system Ab-Or. In general, the attainment of the stable equilibrium solvus (binodal) requires that one phase approach the binodal from outside; for compositions with < 30 mole % Or this phase becomes more potassic with time, with > 30 mole % Or, more sodic. Homogeneous gels of bulk composition Ab70Or30 initially crystallize feldspar pairs inside the binodal, which rapidly (< 17 hours) unmix to define a solvus-like curve (probably the spinodal, with an apparent critical point at 602 °C and 31 mole % Or) and then unmix slowly, giving a solvus after 3000 hours with a critical point at 657 °C and 36 mole % Or.

Because this curve has been approached from two directions it is the best approximation to the binodal (metastable only with respect to Al-Si order) obtained. It is similar to the 2 kbar ‘peralkaline’ solvus of Orville, 1963, provided an adjustment for pressure of 16 °C/kbar is made. Differences between solvi determined by Luth and Tuttle (1966) for ‘non-stoichiometric’ bulk compositions may reflect differences in initial crystallization behaviour, as may the breaks in the solvus limbs suggested by Luth et al. (1974).

Type
Research Article
Information
Mineralogical Magazine , Volume 39 , Issue 307 , September 1974 , pp. 747 - 767
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1974

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bowen, (N. L.) and Tuttle, (O. F.), 1950. Journ. Geol., 58, 489.CrossRefGoogle Scholar
Bachinski, (S. W.) and Müller, (G.), 1971. Journ. Petrology, 12, 329.CrossRefGoogle Scholar
Eugster, (H. P.), Albee, (A. L.), Bence, (A. E.), Thompson, (J. B.), and Waldbnum, (D. R.), 1972. Ibid. 13, 147.CrossRefGoogle Scholar
Goldsmith, (J. R.) and Newton, (R. C.), 1974. The Feldspars, 337; eds. Mackenzie, (W. S.) and Zussman, (J.); Manchester University Press.Google Scholar
Hamilton, (D. L.) and Mackenzie, (W. S.), 1960. Journ. Petrology, 1, 56.CrossRefGoogle Scholar
Luth, (W. C.), 1974. The Feldspars, 249; eds. Mackenzie, (W. S.) and Zussman, (J.); Manchester University Press.Google Scholar
Luth, (W. C.) Martin, (R. F.), and Fenn, (P. M.), 1974. Ibid. 297.Google Scholar
Luth, (W. C.) and Tuttle, (O. F.), 1966. Amer. Min., 51, 1359.Google Scholar
Mackenzie, (W. S.), 1957. Amer. Journ. Sci., 251,481.Google Scholar
Martin, (R. F.), 1969. Contr. Min. Petr., 23,323.CrossRefGoogle Scholar
Morse, (S. A.), :97o, Journ. Petrology, 11, 221.CrossRefGoogle Scholar
Orville, (P. M.), 1963. Amer. .four. Sei., 261, 201.Google Scholar
Owen, (D. C.) and Mcconnell, (J. D.), 1971. Nature (Phys. Sci.), 230, 118.CrossRefGoogle Scholar
Parsons, (I.), 19682. Min. Mag., 36, 797.Google Scholar
Parsons, (I.) 1968b. Ibid. 1061.Google Scholar
Parsons, (I.) 1969. Ibid. 37, 173.CrossRefGoogle Scholar
Piwlnskii, (A. J.) and Martin, (R. F.), 1970. Contr. Min. Petr., 29, 1.CrossRefGoogle Scholar
Roy, (R.), 1956. Journ. Amer. Ceram. Soc., 39, 145.CrossRefGoogle Scholar
Schairer, (J. F.), 1950. Journ. Geol., 58, 512.CrossRefGoogle Scholar
Seck, (H. A.), 1972. Fortschr. Min., 49, 31.Google Scholar
Smith, (J. V.) and Mackenzie, (W. S.), 1961. Estudios Geologicos, Cursillos y Conferencias, 8, 39.Google Scholar
Thompson, (J. B.) and Waldbaum, (D. R.), 1968. Amer. Min., 53,1965.Google Scholar
Thompson, (J. B.) 1969. Ibid. 54, 811.Google Scholar
Trembath, (L. T.), 1973. Min. Mag., 39, 455.CrossRefGoogle Scholar
Tuttle, (O. F.) and Bowen, (N. L.), 1958. Geol. Soc. Amer. Mere., 74.Google Scholar
Waldbaum, (D. R.) and Trtompson, (J. B.), :969. Amer. Min., 54, 1274.Google Scholar
Wright, (T. L.), 1968. Ibid. 53, 88.CrossRefGoogle Scholar
Yund, (R. A.) and Mcallister, (R. H.), 1970. Chem. Geol. 6, 5.Google Scholar