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Local fluctuations in feldspar frameworks

Published online by Cambridge University Press:  05 July 2018

Stuart A. Hayward ,
Ekhard K. H. Salje  and
Jutta Chrosch
Stuart A. Hayward
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
Ekhard K. H. Salje
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK IRC in Superconductivity, Madingley Road, Cambridge, CB3 0HE, UK
Jutta Chrosch
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK IRC in Superconductivity, Madingley Road, Cambridge, CB3 0HE, UK
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Abstract

At any set of thermodynamic conditions a mineral will have some well defined equilibrium crystal structure. However, this structure can be locally disturbed by crystal defects, such as domain walls or solute atoms. This distorted structure will only affect a finite volume within the crystal, but the need to retain continuity within the crystal means that this volume must be non-zero. This means, for example, that the boundary between two domains will include a transition zone from one domain's crystal structure to that of the other domain. Thick twin domain walls can be studied quantitatively, by measuring the intensity of diffuse diffraction between pairs of twin-related Bragg peaks. In alkali feldspar (Or30) at room temperature, these walls are approximately 25 Å thick. Similarly, a single solute atom in a mineral will only affect a small region within a crystal. As a result, chemical mixing will only occur in a substitutional solid solution once there is significant overlap between the strain fields around individual solute atoms. This causes the ‘plateau effect’, where the properties of a phase transition are independent of composition. In alkali feldspar, this plateau extends from albite to 2% Or, which corresponds to a strain field radius of 10 Å.

These phenomena can be modelled using Ginzburg-Landau theory, which predicts that the range of these strain fields will increase as the temperature is raised to Tc. This has been confirmed by measuring the thickness of twin walls as a function of temperature.

Keywords

feldsparcrystal structureframeworklocal fluctuations
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 5 , October 1998 , pp. 639 - 645
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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Footnotes

*

Present address: Departamento de Fisica de la Materia Condensada, Universidad de Sevilla, PO Box 1065, E41080 Sevilla, Spain.

References

Eshelby, J.D. (1956) Continum theory of defects. Solid State Phys., 3, 79–144.CrossRefGoogle Scholar
Harrison, R.J. and Salje, E.K.H. (1994) X-ray diffraction study of the displacive phase transition in anorthoclase, grain-size effects and surface relaxations. Phys. Chem. Minerals., 21, 325–9.CrossRefGoogle Scholar
Hayward, S.A. and Salje, E.K.H. (1996) Displacive phase transition in anorthoclase: the “plateau effect” and the effect of T1/T2 ordering on the transition temperature. Amer. Mineral., 81, 1332–6.CrossRefGoogle Scholar
Hayward, S.A., Chrosch, J., Salje, E.K.H. and Carpenter, M.A. (1996) Determination of the thickness of twin walls in anorthoclase: an X-ray diffraction study. Eur. J. Mineral., 8, 1301–10.CrossRefGoogle Scholar
Heine, V. and McConnell, J.D.C. (1981) Origin of modulated incommensurate phases in insulators. Phys. Rev. Lett., 46, 1092–5.CrossRefGoogle Scholar
Heine, V. and McConnell, J.D.C. (1984) The origin of incommensurate structures in insulators. J. Phys. C., 17, 1199–220.CrossRefGoogle Scholar
Ilyama, J.T. and Volfinger, M. (1976) A model of trace-element distribution in silicate structures. Mineral. Mag., 40, 555–64.Google Scholar
Kroll, H.R. (1983) Thermal expansion of alkali feldspars. In Feldspars and Feldspathoid.(Brown, W.L., ed.), Reidel, Dordrecht, pp. 163–206.Google Scholar
Landau, L.D. and Lifshitz, E.M. (1986) Theory of Elasticity. Pergamon, Oxford.Google Scholar
Locherer, K.R., Hayward, S.A., Hirst, P.J., Chrosch, J., Yeadon, M., Abell, J.S. and Salje, E.K.H. (1996) Xray analysis of mesoscopic twin structures. Phil. Trans. R. Soc. Lon. A, 354, 2815–45.Google Scholar
Newton, R.C. and Wood, B.J. (1980) Volume behaviour of silicate solid solutions. Amer. Mineral., 65, 733–45.Google Scholar
Okamura, F.P. and Ghose, S. (1975) Analbite → monalbite transition in a heat treated amelia albite. Contrib. Mineral. Petrol., 50, 211–6.CrossRefGoogle Scholar
Salje, E.K.H. (1990) Phase Transitions in Ferroelastic and Co-elastic Crystals. Cambridge University Press, Cambridge.Google Scholar
Salje, E.K.H. (1995) A novel 7-circle diffractometer for the rapid analysis of extended defects in thin films, single crystals and ceramics. Phase Transitions, 55, 37–56.CrossRefGoogle Scholar
Salje, E.K.H., Kuscholke, B., Wruck, B. and Kroll, H. (1985) Thermodynamics of sodium feldspar II: Experimental results and numerical calculations. Phys. Chem. Minerals, 12, 99–107.CrossRefGoogle Scholar
Slimming, E.H. (1976) An electron diffraction study of some intermediate plagioclases. Amer. Mineral., 61, 54–9.Google Scholar
Teodisu, C. (1982) Elastic Models of Crystal Defects. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Voronkova, V.I. and Wolf, T. (1993) Thermomechanical detwinning of YBa2Cu3O7–x single crystals under reduced oxygen partial pressure. Physica C, 218, 175–80.CrossRefGoogle Scholar
Yund, R.A., Smith, B.M. and Tullis, J. (1981) Dislocation-assisted diffusion of oxygen in albite. Phys. Chem. Minerals, 7, 185–9.CrossRefGoogle Scholar
Yund, R.A., Quigley, J. and Tullis, J. (1989) The effect of dislocations on bulk diffusion in feldspars during metamorphism. J. Metam. Geol., 7, 337–41.CrossRefGoogle Scholar
Zhang, M., Wruck, B., Graeme-Barber, A. and Salje, E.K.H. (1996) Phonon spectra of alkali feldspars: phase transitions and solid solutions. Amer. Mineral., 81, 92–104.CrossRefGoogle Scholar