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A granophyre from Coire Uaigneich, Isle of Skye, containing quartz paramorphs after tridymite (Plate XIII)

Published online by Cambridge University Press:  14 March 2018

L. R. Wager ,
D. S. Weedon  and
E. A. Vincent
L. R. Wager
Affiliation:
Department of Geology and Mineralogy, University Museum, Oxford
D. S. Weedon
Affiliation:
Department of Geology and Mineralogy, University Museum, Oxford
E. A. Vincent
Affiliation:
Department of Geology and Mineralogy, University Museum, Oxford
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Extract

The narrow belt of granophyre lying to the west of Blaven in the Isle of Skye showed so admirably the effects of chilling that a series of specimens was collected by one of us (L.R.W.) and found to contain, in the chilled marginal rock, phenoerysts of tridymite, now inverted to quartz. In the Thulean Tertiary igneous province former tridymite is known from certain acid lavas, for example, the Tardree rhyolite (von Lasaulx, 1877) and certain Icelandic liparites (Hawkes, 1916), and from metamorphosed arkoses adjacent to basic igneous intrusions (Harker, 1908, 1932), but it has not previously been noted in the intrusive acid rocks. In addition to phenocrysts of tridymite inverted to quartz, there is present in the groundmass of the unchilled granophyre a second generation of inverted tridymite crystals, surrounded by a final stage of quartz and felspar which has crystallized with normal microgranitic textures. Some of the textural features resemble those of the normal Skye granophyres, while others resemble certain metamorphosed arkoses.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 30 , Issue 223 , December 1953 , pp. 263 - 276
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1953

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