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The variable composition of cordierite in the Dartmoor granites

Published online by Cambridge University Press:  14 March 2018

A. Brammall  and
B. Rama Rao
A. Brammall
Affiliation:
Geological Department, Imperial College of Science and Technology, London
B. Rama Rao
Affiliation:
Geological Department, Imperial College of Science and Technology, London
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Extract

The recognition of pronounced varietalism in both the garnet and the basic mica of the Dartmoor granites prompted the authors to inquire whether the cordierite associated with these species was similarly variable in composition.

The inquiry was directed in the first instance to possible variation in the optic axial angle 2V, which is determinable with accuracy on the unaltered parts of cordierite in thin rock sections. Determinations made on the sector-twinned cordierites in the garnetiferous granite of Sweltor a gave the following peculiar results, which Mr. Rama Rao verified repeatedly, using a Fedorov microscope in perfect adjustment.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 24 , Issue 152 , March 1936 , pp. 257 - 259
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1936

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References

page 257 note 1 Brammall, A. and Bracewell, S., Min. Mag., 1936, vol. 24 Google Scholar (preceding paper).

page 257 note 2 Brammall, A. and Harwood, H. F., Quart. Journ. Geol. Soc. London, 1932, vol. 88, pp. 184 CrossRefGoogle Scholar, 217, and fig. 19, p. 215.

page 257 note 3 Loc. cit., 1932, fig. 6, p. 187.

page 257 note 4 Loc. cit., 1932, p. 186.