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A blue sodic beryl from southeast Ireland

Published online by Cambridge University Press:  05 July 2018

I. S. Sanders  and
D. H. Doff
I. S. Sanders
Affiliation:
Department of Geology, Trinity College, Dublin 2, Ireland
D. H. Doff
Affiliation:
Department of Geology, Trinity College, Dublin 2, Ireland
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Abstract

Deep azure-blue beryl is reported from veins in Upper Devonian conglomerate from southeast Ireland. Microprobe analysis, Mössbauer spectroscopy and loss on ignition suggest an unusual chemistry with an exceptionally high degree of substitution of Fe and Mg for Al, and extreme amounts of Na and water held within channel sites in the structure. The calculated structural formula is:

Refractive indices (1.603 and 1.595) and the cell edge, a, (9.292 Å) are also unusually high. Colourless beryl from the same locality, some of which forms cores to blue beryl prisms, has less octahedral substitution and a lower Fe/Mg ratio. The origin of the beryl is tentatively linked to contemporaneous volcanic activity.

Keywords

berylMössbauer spectroscopysodiumIreland
Type
Mineralogy and Geochemistry
Information
Mineralogical Magazine , Volume 55 , Issue 379 , June 1991 , pp. 167 - 172
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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