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The blue coloration in banded fluorite (Blue John) from Castleton, Derbyshire, England

Published online by Cambridge University Press:  05 July 2018

A. K. Galwey ,
K. A. Jones ,
R. Reed  and
D. Dollimore
A. K. Galwey
Affiliation:
Department of Chemistry, The Queen's University, Belfast BT7 1NN, Northern, Ireland
K. A. Jones
Affiliation:
Department of Geology, The Queen's University, Belfast BT7 1NN, Northern, Ireland
R. Reed
Affiliation:
The Electron Microscopy Laboratory, The Queen's University, Belfast BT7 1NN, Northern, Ireland
D. Dollimore
Affiliation:
Department of Chemistry and Applied Chemistry, University of Salford, Salford, M5 4WT, LancashireEngland
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Summary

From the microscopic examination of lightly etched, cleaved (111) surfaces of banded blue fluorite (Blue John, from Castleton, Derbyshire) it is concluded that the coloured lamellae are not necessarily or exclusively associated with lattice-line imperfections. Elemental analyses, by electron dispersive methods, of fresh cleavage (111) surfaces in the immediate vicinity of small inclusions (c. 10 µm diameter) possessing associated coloured haloes detected no appreciable concentrations of impurities. From the evidence available, it is suggested that the zones of blue colour consist of colloidal calcium resulting from radiation damage caused by the intermittent deposition of radioactive material on the surfaces of fluorite during crystal development. The dispersion of colloidal calcium produced is particularly stable as a consequence of the close correspondence between lattice spacings in calcium fluoride and in calcium metal.

Type
Research Article
Information
Mineralogical Magazine , Volume 43 , Issue 326 , June 1979 , pp. 243 - 250
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1979

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References

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