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On the Relations between the Solution-planes of Crystals and those of Secondary Twinning; and on the Mode of Development of Negative Crystals along the Former. A Contribution to the Theory of Schillerization
Published online by Cambridge University Press: 14 March 2018
Extract
In the case of many common rock-forming minerals—the felspars, the pyroxenes, the olivines and the micas—it has been shown that the crystals which have existed in rock-masses at great depths exhibit constant and characteristic differences from the crystals of the same mineral, in rocks of identical composition, which have been formed at the surface. It has been proved, moreover, that these differences become mere and more pronounced in proportion to the distance from the surface at which these rocks have originally existed.
Although some of these peculiarities of the crystals of deep-seated rockmasses can be satisfactorily accounted for by the conditions of pressure and slow growth under which they were originally formed, yet there are others—and these by no means the least striking of them, such as the continuous bands of fluid-enclosures, the avanturine structure and schiller, and the chatoyant phenomena—which are clearly not original, but are due to secondary actions.
- Type
- Research Article
- Information
- Mineralogical magazine and journal of the Mineralogical Society , Volume 7 , Issue 33 , December 1886 , pp. 81 - 92
- Copyright
- Copyright © The Mineralogical Society of Great Britain and Ireland 1886
References
page 81 note * Quart. Journ. Geol. Soc. Vol XLI. (1885), pp. 374-389.
page 81 note † Loc. cit. Plates X. to XII. with description.
page 81 note ‡ Mr. G. H. Williams, in his very interesting paper on “The Peridotites of the Cortlandt Series,” in the American Journal of Science for January 1886, has written under some misapprehension of the arguments of my paper. That certain enclosures in minerals are original and were formed during the growth of the crystals, I have never deniled. My arguments were intended to apply to the cases of those enclosures which I have proved, by the most conclusive evidence, to be of secondary origin. When we find structures developed having unmistakeable relations with the accidental fissures of a crystal, it is as impossible to deny their secondary origin as it is to doubt that the serpentine found bounding the accidental cracks in a crystal of olivine was formed long subsequently to t he crystallisation of the olivine itself.
page 84 note * Die Lösungsflachen des Kalkspathes und des Aragonites. I.DieLösungsflilchen und Losungsgestalten des Kalkspathes (Sitzber. der Kais. Wiener Akad. der Wissensch. 89 Bd. II. Abth. 1884), pp. 368-458. II. Die Ätzfiguren des Kalkspathes. III. Die Lösungsflachen des Aragonites (Sitzber. der Kais. Wiener. Akad. der Wissensch. Bd, 91. IL Abth). (1885), pp. 760-835.
page 85 note * Quart. Journ. Geol. Soc. Vol. XLL (1885), p. 385.
page 87 note * Quart. Journ. Geol. Soc. Vol. XLI. (1885), p, 382. Plate XII. Figs. 4 and 5.
page 87 note † Neues Jahrb.för Min. 1883, 1. p. 32.
page 87 note ‡ Ibid. 1886. p. 185.
page 87 note § Quart. Journ. Geol. Soc. Vol. XLI. (1885), p. 379.
page 88 note * BuU. Soc. Min. Fr. II. (1879), p. 113.
page 88 note † Quart. Journ. Geol. Soc. Vol. XLI. (1885). PI. X. F. 7, pp. 376, 377.
page 88 note ‡ The crystals of these granulitic rocks often exhibit a peculiarity, for which I do not at present find myself able to suggest any explanation. An irregular outer zone of the rounded crystals appears to be free from the secondary inclusions which are beautifully developed in their central portions. This peculiarity is not exhibited by rocks with a granitic structure.