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Plagioclases from the Juvinas meteorite and from allivalite from the Isle of Rhum

Published online by Cambridge University Press:  14 March 2018

P. M. Game
P. M. Game*
Affiliation:
Department of Mineralogy, British Museum (Natural History)
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Summary

The optical properties and specific gravity, and the variations in these properties, of analysed plagioclases separated from the meteorite (eucrite) from Juvinas, France, are compared with the corresponding values for a terrestrial plagioclase of almost identical composition from an allivalite from Rhum. The range in properties for the Juvinas plagioclase indicates a compositional range from about Ab35An65 to Ab15An85, but the great majority of grains are bytownite with approximately 83 % (molecular) anorthite.

The frequency of occurrence of the twin-laws of the Juvinas plagioclase resembles that of plagioclase from basalts and allied rocks.

The variable changes and, in some grains, absence of change in the optical properties shown by the Juvinas plagioclase crystals, after heating to 1100°C. for 48 hours followed by rapid cooling, contrasts with the small but constant optical changes shown by the allivalite plagioclase (for which geological evidence indicates slow cooling) after identical heat treatment. It is inferred that the meteoritic plagioclase grains have had differing thermal histories, and that some grains have been subjected to previous natural quenching.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 31 , Issue 239 , December 1957 , pp. 656 - 671
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1957

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References

page 657 note 1 Kindly sent by H. W. Fairbairn of the Massachusetts Institute of Technology.

page 657 note 2 See, for example, H. Tertsch, Tschermaks Min. Petr. Mitt. 1941, vol. 53, p. 56.

page 658 note 1 Min. Mag. 1957, vol. 31, p. 426.

page 659 note 1 In this and all subsequent standard deviations, the small sample correction has been applied.

page 660 note 1 Die Fedorow-Methode. Berlin, 1936, fig. vi.

page 660 note 2 Uaiversaldrehtischmethoden. Basel, 1931.

page 660 note 3 These curves are drawn on a stereographie projection of radius 10 cm.

page 661 note 1 Composition derived from the curves by H. Tertsch, Tschermaks Min. Pert. Mitt., 1942, eel. 54, figs. 4a and 6a. The An percentages are based on the high temperature curves because of the greater consistency in the values interpolated on these curves rather than on the low temperature curves.

page 669 note 1 G. C. Kennedy, Amer. Min., 1947, vol. 32, p. 562, fig. 1 [M.A. 10-267]; F. Chayes, Amer. Journ. Sci., 1952, Bowen vol., pt. 1, p. 96, table 5 [M.A. 12-134l; R. M. Crump and K. B. Ketner, Mem. Geol. Soc. Amer., 1953, no. 52, p. 31, fig. 6; A. N. Winehell and H. Winchell, Elements of Optical Mineralogy, 4th edn, 1951, pt. 2, p. 316; E. Wenk, Schweiz. Min. Petr. Mitt., 1945, vol. 25, p. 369, fig. 1 ; A. Poldervaart, Amer. Mira, 1950, vol. 35, p. 1069, fig. 1 [M.A. 11-389] ; H. Tertsch, Tschermaks Min. Petr. Mitt., 1942. vol. 54, p. 206, fig. 4a, and p. 208, fig. 5a [M.A. 9-270].

page 670 note 1 C. T. Barber, Mere. Geol. Surv. India, 1936, vol. 68, pt. 2, p. 224, table 6 [M.A. 7-21]; M. Gorai, Amer. Min., 1951, vo]. 36, p. 885, table 1 [M.A. 11-489l; W. Larsson, Bull. Geol. Inst. Univ. Upsala, 1941, vol. 28, p. 373 [M.A. 9-177]; G. Paliuc, Sehweiz. Min. Petr. Mitt., 1932, vol. 12, p. 428 [M.A. 5-436]; W. R. Chapman, Amer. Min., 1936, vol. 21, p. 39, table 2 [M.A. 6-293] ; A. Vendl, Tsehermaks Min. Petr. Mitt., 1931, vol. 42, pp. 491-550; Vendl’s results summarized by H. Wieseneder, ibid., 1933, vol. 44, p. 203.

page 670 note 2 Mem. Geol. Soc. Amer., 1953, vol. 52, p. 42.

page 671 note 1 Phil. Trans. Roy. Soc., 1956, set. B, vol. 240, p. 48.

page 671 note 2 Min. Mag., vol. 30, 1954, table 1, p. 433.