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Note on some Specimens of Glaucophane-Rock from the Ile de Groix
Published online by Cambridge University Press: 14 March 2018
Extract
In my description of a Glaucophane-eclogite from the val d' Aoste, I alluded to the occurrence of a rather similar rock in the Ile de Groix (off the south coast of Brittany) in the following words:—" In the Ile de Groix the glaueophane occurs in no great abundance, with greenish mica, epidote, garnet, hornblende, and but little quartz." My knowledge of the rock, as then stated, was from one or two specimens only; but in the autumn of 1886 I paid a short visit to the Ile de Groix in order to see the rock in the field. I then found that in the above phrase I had unwittingly done an injustice to this locality for glaucophane, for I obtained specimens in which that mineral is even more abundant and almost as well developed as in the rock from the Val d' Aoste. On this account, and as the locality is rarely visited, I venture to think that a few notes may be interesting to the Society, although the rock has been already excellently discussed by Dr. Charles Barrois, to whom I am much indebted for information about this and other interesting localities in Brittany.
- Type
- Research Article
- Information
- Mineralogical magazine and journal of the Mineralogical Society , Volume 7 , Issue 34 , July 1887 , pp. 150 - 154
- Copyright
- Copyright © The Mineralogical Society of Great Britain and Ireland 1887
References
page 150 note 1 Min. Mag. Vol. VII., p. 1.
page 150 note 2 It can be reached by a steamer from Lorient. As this starts about 6 a.m. it would be possible to visit some of the localities and get back the same evening to Lorient, but it is better to pass the night in the Island. Near the landing place is an auberge ; the entertainment is homely but the people are kindly.
page 150 note 3 Annales de la Soc. Géol. du Nord. Vol. XI. p. 18.
page 150 note 4 Presidential Address to the Geol. Soc. 1886. See Proceedings, Vol. XLII.
page 151 note 1 e.g. Apparently above the rather friable banded gneisses, as on the south side of the St. Gothard group.
page 151 note 2 Otherwise I should have retained the name eclogile. used in my last paper; for in all the specimens noticed in this garnet is present abundantly.
page 151 note 3 Hather large but ill-preserved crystals of andalusite are developed near the junction of the rocks, chiefly in the mica-schist; possibly this may be indicative of an intrusion.
page 152 note 1 Both magnetite and hematite occur variably.
page 153 note 1 They might be of secondary origin, formed by solution of the garnet along lines of strain ; but if this were so, it would be difficult to explain their being bent into S-like folds, as they are in at least two of the garnets.
page 153 note 2 Journal of the College of Science, Imperial Univ. Vol. I. Part I, (1886).
page 154 note 1 I have not noticed any change in my slides; those from the Val d’ Aoste are guite eighteen months old.