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Tourmalinization in the Dartmoor granite

Published online by Cambridge University Press:  14 March 2018

A. Brammall  and
H. F. Harwood
A. Brammall
Affiliation:
Imperial College of Science and Technology, London
H. F. Harwood
Affiliation:
Imperial College of Science and Technology, London
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Extract

On the basis of field relationships, the main types of the Dartmoor granite can be referred to four stages of intrusion, the sequence being from relatively basic to thoroughly acid.

To this sequence is closely related an increase in the content of tourmaline and in the extent to which autopneumatolysis (with tourmalinization) was effective before solidification of the rock was complete.

Autopneumatolysis is well displayed by many minor intrusions referred to the latest stage. Such an intrusive rock is reddened more or less uniformly throughout its entire mass, and volatile constituents exhaled from its margin have reddened a contact-zone of the grey granite into which it is intrusive.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 20 , Issue 109 , June 1925 , pp. 319 - 330
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1925

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References

Page 319 note 1 Brammall, A. and Harwood, H. F., The Dartmoor granite : its mineralogy strueture, and petrology. Min. Mag., 1923, vol. 207, p. 53 Google Scholar.

Page 319 note 2 Brammall, A. and Harwood, H. F., The occurrence of rutile, brookite, and anatase on Dartmoor. Min. Mag., 1923, vol. 20, pp. 23–24 CrossRefGoogle Scholar.

Page 321 note 1 A. Brammall and H. F. Harwood, loc. cit., pp. 22-23.

Page 325 note 1 Compare tile following blowpipe reactions. In the borax bead all silicates are fluxed. In microcosmic salt all silicates except the borosilicates (e. g. tourmaline and axinite) leave an infusible residue of silica.

Page 328 note 1 A. Brammall and H. F. Harwood, loc. cit., 1923, p. 23.

Page 328 note 2 Dana's ‘System of Mineralogy’, 6th ed., 1892, pp. 554-5, analyses nos. 15, 16, 17, 27, and 33.