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The structures of the plagioclase felspars: VII. The heat treatment of intermediate plagioclases1

Published online by Cambridge University Press:  14 March 2018

P. Gay  and
M. G. Bown
P. Gay
Affiliation:
Department of Mineralogy and Petrology, Cambridge
M. G. Bown
Affiliation:
Department of Mineralogy and Petrology, Cambridge
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Summary

Previous work has established that natural ‘low-temperature’ intermediate plagioclases show single-crystal diffraction patterns in which the subsidiary reflections are split into two; the separation of these split reflections appears to be dependent on the composition of the felspar. Several of these specimens have been subjected to varying heat treatments and their diffraction patterns examined.

It is found that over the whole composition range the split subsidiary reflections have disappeared after treatment at high temperatures, and only the principal felspar reflections, which are characteristic of an albite-like structure, remain. Natural specimens initially showing anomalous patterns can also be homogenized in this way by suitable heat treatments. A careful study of the mode of disappearance shows that the separation of the subsidiary reflections is unchanged as long as they remain visible.

The structural and petrological implications of this work are discussed.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 31 , Issue 235 , December 1956 , pp. 306 - 313
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1956

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Footnotes

1

Part VI, Min. Mag., 1956, vol. 31, p. 21.

References

Cole, (W. F.), Sörum, (H.), and Taylor, (W. H.), 1951. Acta Cryst., vol. 4, p. 20. [M.A. 11-427.]Google Scholar
Gay, (P.), 1953. Min. Mag., vol. 30, p. 169.Google Scholar
Gay, (P.), 1954. Ibid., vol. 30, p. 248.Google Scholar
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Goodyear, (J.) and Duffin, (W. J.), 1954. Ibid., vol. 30, p. 306.Google Scholar
Kracek, (F. C.) and Neuvonen, (K. J.), 1952. Amer. Journ. Sci., Bowen volume, p. 293. [M.A. 12-134.]Google Scholar
Muir, (I. D.), 1955. Min. Mag., vol. 30, p. 545.Google Scholar
Smith, (J. V.), 1956. Ibid., vol. 31, p. 47.Google Scholar