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The influence of chemical factors on the crystallization of hornblende in igneous rocks

Published online by Cambridge University Press:  14 March 2018

W. Q. Kennedy
W. Q. Kennedy*
Affiliation:
H.M., Geological Survey of Great Britain
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Extract

It is now more than sixty years since Tschermak first published his classical paper on the relationship between the pyroxenes and amphiboles, but, in spite of our greatly increased knowledge of these important rock-forming minerals, many of the problems concerning their constitution and genesis remain unsolved. In particular, the nature of the conditions which determine whether a pyroxene or an amphibole will separate from a crystallizing magma are imperfectly understood, although the point is one of very considerable petrological significance. Much fuller information is necessary, particularly with regard to the relationship between the composition of the ferromagnesian minerals and the rocks in which they occur. The present paper merely represents a preliminary attempt to correlate the available chemical evidence and to determine what other possible factors might influence the character of the ferromagnesian crystallization.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 24 , Issue 151 , December 1935 , pp. 203 - 207
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1935

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References

page 203 note 1 Tschermak, G., Beziehung zwischen der Pyroxen- und Amphibolgruppe. Min. Mitt., 1871, p. 17.Google Scholar

page 204 note 1 Eitel, W., Die Mischkristallbildung in der Gruppe der alkali- und tonerdhaltigen Hornblenden... Neues Jahrb. Min., 1922, Beil.-Bd. 47, pp. 214-217.Google Scholar

page 204 note 2 Kunitz, W., Die Isomorphieverhäiltnisse in der Hornblendegruppe. Neues Jahrb. Min., Abt. A, 1930, Beil.-Bd. 60, pp. 173-174.Google Scholar [M.A. 4-200.]

page 204 note 3 Niggli, p., Gesteins und Mineralprovinzen. Berlin, 1923, pp. 77-78.Google Scholar

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page 206 note 2 His method of calculation was as follows (loc. cit., 1923, pp. 75-78). In rocks containing remit silicates completely dominated by abundant pyroxene, the metasilicate proportions of the modal pyroxene were obtained by allotting CaO for anorthite, &c., and Fee for magnetite, &c. The remaining MgO, CaO, and Fee was then recalculated to 100, and the proportions tbtaincd were plotted in the diagram. The same method was employed in the calculation of the analyses of pyroxenes.

page 206 note 3 Warren, B. E., Zeits. Krist., 1930. vol. 72, p.493.Google Scholar [M.A. 4-278.]

page 207 note 1 These represent the available analyses of hornblendes from igneous rocks quoted from the following sources :- Doelter, C., Handbuch der Mineralchemie, 1912-14, vol. 2 (I), pp. 586-649 ;Google Scholar Rosenbusch, H., Elemente der Gesteinslehre, 4th edition, 1923 ; W. Kunitz, loc. cit., 1930, pp. 171-250.Google Scholar

page 207 note 2 W. Q. Kennedy and H. H. Read, The differentiated dyke of Newmains, Dumfriesshire ... Quart. Journ. Geol. Soc. London (in the press).