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The Dartmoor granite: its mineralogy, structure, and petrology1

Published online by Cambridge University Press:  14 March 2018

Alfred Brammall  and
H. F. Harwood
Alfred 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

This paper continues the study of the constituent minerals of the Dartmoor granite. The district to which it mainly refers comprises the for-area around Widecombe and a part of the aureole adjoining. No detailed reference will be made at this stage to aureole phenomena. The results to be recorded necessitate a brief description of the two main granite types and of their field relationships. Abundant varieties and modifications of both types occur, but for the Purposes of the present paper they are of subordinate importance.

Most of the for-masses and high-level exposures of granite in the area consist in the main of the type known locally as the ‘giant granite‘ — a very coarse-grained, strongly porphyritic roelc rich in biotite, and consistently garnetiferous; it has an index-figure 1 ranging from 7.5 to 12.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 20 , Issue 101 , June 1923 , pp. 39 - 53
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1923

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Footnotes

1

Previous papers of this series (this vol., pp. 20 and 27) dealt with the minerals rutile, brookite, anatase, and zircon.

References

Page 39 note 1 For a general description of the granite and of its varieties, see ‘The Geology of Dartmoor’ (Mere. Geol. Survey), 1912, pp. 27-43.

Page 40 note 1 The term ‘index-figure’ is used to express the average percentage by weight of mineral grains of sp. gr. > 2.86 obtainable from crushed rock material which has been washed free from rock-flour. The raw material passes a sieve with 40 wires to the linear inch.

Page 43 note 1 ‘The Geology of Dartmoor’ (Mem. Geol. Survey), 1912, pp. 31, 39-40.

Page 46 note 1 ‘The Geology of Dartmoor’ (Mere. Geol. Survey), 1912, pp. 30, 32. and 34.

Page 46 note 2 Idem, pp. 41-42.

Page 47 note 1 For descriptions, and references to literature, see Survey Memoir (Dartmoor), pp. 45-46 ; also p. 102, plate 1, fig. 3.

Page 48 note 1 Survey Memoir (Dartmoor), p. 45.

Page 50 note 1 See also Survey Memoir (Dartmoor), p. 33.

Page 51 note 1 C. A., McMahon, ‘Notes on Dartmoor.’ Quart. Journ. Geol. Soc., 1893, vol. 49, p. 886 Google Scholar.

Page 51 note 2 Survey Memoir (Dartmoor), p. 40.

Page 53 note 1 Survey Memoir (Dartmoor), p. 27.