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On a Glaucophane-eclogite from the Val d'Aoste

Published online by Cambridge University Press:  14 March 2018

T. G. Bonney
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Extract

The number of localities at which glaucophane has been discovered is still comparatively small, so that it may be of interest to add another and to describe the microscopic structure of a rock in which this interesting variety of hornblende occurs.

The carriage road between Vertex and St. "Vincent in the Val d' Aoste mounts along the left bank of the Dora Baltea, which, in one part, often called the defile of Mont Jovet, is scarped and craggy. The steepest part of the ascent is between the hamlets of Berrioz and Nus (?). I was walking up this, one day in July 1885, in company with my friend the Rev. E. Hill, F.G.S., when my eye fell upon a rock, which I at once reeognised as a variety of eclogite, composed chiefly of small reddish garnets and dull-green hornblende. We secured specimens, though with considerable difficulty, for the rock was very tough ; made a few observations and passed on.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 7 , Issue 32 , July 1886 , pp. 1 - 8
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1886

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References

page 4 note * The word is used in its strict sense.

page 4 note † Unfortunately I omitted to record the thickness of the exposure, but it is certainly several feet at least.

page 5 note * I hope the next visitor will endeavour to work this out. As it may prove, if it can be done, a rather long task, he had better sleep at St. Vincent, where the hotels are much better than at Verrex : if the roads are dusty he had better take a brush with him. He cannot miss the locality, it is on his left hand as he descends the high road.

page 5 note † Geol. Mag. Dec. II. Vol. VI. p. 363.

page 5 note ‡ Mr. G. H. Williams (N. J. 1882, Bd. II. p. 201) notices a rock which he believes to be from this locality (of this I am doubtful), and intimates that I should have called it an amphibolite. As in 1879 it was not even certain that amphibolite denoted an igneous rock (I am not aware that there is harmony in its use now), and as I was satisfied the rock was of igneous origin, and had once been a gabbro, I preferred to call it (as I shall continue to do) a glaucophane-gabbro.

page 6 note * See also Atti R. Accad. Lincei, Ser. 2, Vol. II. p. 333. Here it is said that the specimens from the Val d’ Aoste “furono estratti dagli affioramenti dei depositi cupriferi di Champ de Praz e S. Marcello.” I cannot find on ray maps the former place, but, as the latter is between Chatillon and Aosta, conclude the above localities are different from that which I have described. In this memoir the optical properties are described.

page 7 note * I am indebted to the President and Mr. T. Davies for the opportunity of studying the slides, &c. mentioned in this paragraph.

page 7 note † I have a specimen of this and of the Syra rook in my own collection, for which I am indebted to Prof. Judd.