Enthalpies of ordering in the plagioclase feldspar solid solution

Carpenter, Michael A.; McConnell, J. D. C.; Navrotsky, Alexandra

doi:10.1016/0016-7037(85)90310-2

Cited by 98 publications

(55 citation statements)

References 47 publications

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“…This is the same volcanic sample as characterised by Carpenter et al (1985), with an anorthite content of around 98 % determined by electron microprobe analysis. Separated powder was ground and mixed with silicon as an internal standard.…”

Section: Methodsmentioning

confidence: 99%

Thermodynamics of plagioclase III: Spontaneous strain at the $$I\overline 1 - P\overline 1$$ phase transition in Ca-rich plagioclase

1988

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Abstract. The lattice parameters of anorthites AngsAb 2 and Anloo have been measured from 22 to 1100 K. The spontaneous strain arising from the I1-P 1 displacive transition in An98 follows second order Landau behaviour. The spontaneous strain (es) couples quadratically to the order parameter (QO) with esocQ~ * -T) and T* = 530 K in An98. This is in contrast to the tricritical behaviour observed in pure anorthite. These observations are consistent with a Landau model for the free energy of Ca-rich plagioclases in which A1/Si order and Na content renormalize the fourth order coefficient.

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Section: Methodsmentioning

confidence: 99%

Thermodynamics of plagioclase III: Spontaneous strain at the $$I\overline 1 - P\overline 1$$ phase transition in Ca-rich plagioclase

1988

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“…The effect of Al distribution within T-sites has been widely studied (e.g., Ferguson et al 1958;Ribbe et al 1969;Prewitt et al 1976;Winter et al 1979;Carpenter et al 1985Carpenter et al , 1990Kunz and Armbruster 1990;Sochalski-Kolbus et al 2010), and has been found to play an important role in the topology of the tetrahedral framework. Because Al atoms are larger than Si atoms, the Al-O bonds are longer than Si-O bonds.…”

Section: Structuresmentioning

confidence: 99%

Ab initio calculations of elastic constants of plagioclase feldspars

Kaercher

Militzer

Wenk

2014

American Mineralogist

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Plagioclase feldspars comprise a large portion of the Earth's crust and are very anisotropic, making accurate knowledge of their elastic properties important for understanding the crust's anisotropic seismic signature. However, except for albite, existing elastic constants for plagioclase feldspars are derived from measurements that cannot resolve the triclinic symmetry. We calculate elastic constants for plagioclase end-members albite NaAlSi 3 O 8 and anorthite CaAl 2 Si 2 O 8 and intermediate andesine/ labradorite NaCaAl 3 Si 5 O 16 using density functional theory to compare with and improve existing elastic constants and to study trends in elasticity with changing composition. We obtain elastic constants similar to measured elastic constants and find that anisotropy decreases with anorthite content.

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“…The results of electron microprobe analysis indicate an average composition of An96Ab4, with a range of 2-6% albite amongst different grains. Electron diffraction shows that it displays sharp 'c' and 'd' reflections characteristic of P1 symmetry (Carpenter et al 1985). The process of annealing to produce sample VP/1 induces a small amount of A1/Si disorder and sample 115082 a must be slightly disordered by virtue of its small albite content.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The composition determined by electron microprobe is Anloo. The sample is identical to that labelled Pasmeda/1 by Carpenter et al (1985), but we shall adopt the labelling instituted by Carpenter et al (1990) and refer to it as VP/1.…”

Section: Experimental Methodsmentioning

confidence: 99%

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The effect of Al/Si disorder on the I $$\bar 1$$ -P $$\bar 1$$ Co-Elastic phase transition in Ca-rich plagioclase

Redfern

1992

Phys Chem Minerals

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Abstract. The influence of A1/Si disorder in the anorthite tetrahedral framework upon the I1-P1 displacive transition of that framework has been investigted at high-temperatme by powder X-ray diffraction. The temperaturedependence of the order parameter in a heat-treated (disordered) anorthite and a Ca-rich plagioctase has been determined from spontaneous strain measurements. Both samples show appreciable disorder, with Qoa = 0.88 in both cases. In each, the critical exponent/~ appears to be intermediate between values for classical tricritical (]) and second-order ( 89 phase transitions. This critical behaviour is consistent with a Landau potential in which the coefficient of the quartic term is positive but smaller than the coefficient of the sixth order term, corresponding to a second-order phase transition close to a tricritical point. There does not appear to be any defect strain tail near T~ and inhomogeneities in Qoa appear to be on rather a short length scale in these samples. The role of changing Qoa appears to be more important than that of changing composition (albite component). The data are interpreted using a model of a homogeneous field due to changing Qoa which renormalizes the transition temperature, T*, and the fourth order coefficient, Bell, in the Landau expansion. The results are consistent with classical Landau behaviour, and demonstrate the care which must be taken in interpreting apparently non-classical critical exponents for phase transitions close to a tricritical point.

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Enthalpies of ordering in the plagioclase feldspar solid solution

Cited by 98 publications

References 47 publications

Thermodynamics of plagioclase III: Spontaneous strain at the $$I\overline 1 - P\overline 1$$ phase transition in Ca-rich plagioclase

Thermodynamics of plagioclase III: Spontaneous strain at the $$I\overline 1 - P\overline 1$$ phase transition in Ca-rich plagioclase

Ab initio calculations of elastic constants of plagioclase feldspars

The effect of Al/Si disorder on the I $$\bar 1$$ -P $$\bar 1$$ Co-Elastic phase transition in Ca-rich plagioclase

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