Lattice simulation studies of the ferroelastic phase transitions in (Na,K)AlSi3O8 and (Sr,Ca)Al2Si2O8 feldspar solid solutions

Lattice-energy minimization calculations on these two feldspar systems as functions of composition to simulate the ferroelastic phase transitions I2/c-I and C2/m-C show that these transitions occur as a function of composition and are driven by the vanishing of the quantity C44C66-C 2 46 without any...

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Bibliographic Details
Published in:	The American mineralogist 1997-01, Vol.82 (1-2), p.8-15
Main Authors:	Dove, Martin T, Redfern, Simon A. T
Format:	Article
Language:	eng
Subjects:	alkali feldspar crystal structure feldspar group framework silicates K-feldspar lattice parameters Mineralogy Minerals order-disorder phase equilibria silicates Simulation solid solution thermodynamic properties
Online Access:	Get full text
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Summary:	Lattice-energy minimization calculations on these two feldspar systems as functions of composition to simulate the ferroelastic phase transitions I2/c-I and C2/m-C show that these transitions occur as a function of composition and are driven by the vanishing of the quantity C44C66-C 2 46 without any of the individual elastic components being strongly dependent on composition and without softening of an optic mode. In both cases the strains ε4 and ε4 and ε6 are proportional to each other for small values of strain, but non-linear coupling become dominant when \|ε4\| becomes >> ∼ 0.02. These results are consistent with experimental data and explain the nature of coupling of the displacive transition to Al-Si ordering in Al:Si 2:2 feldspars.
ISSN:	0003-004X 1945-3027