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The cause of the colour of Blue John and other purple fluorites

Published online by Cambridge University Press:  05 July 2018

R. S. W. Braithwaite ,
W. T. Flowers ,
R. N. Haszeldine  and
M. Russell
R. S. W. Braithwaite
Affiliation:
Department of Chemistry, University of Manchester Institute of Science and Technology
W. T. Flowers
Affiliation:
Department of Chemistry, University of Manchester Institute of Science and Technology
R. N. Haszeldine
Affiliation:
Department of Chemistry, University of Manchester Institute of Science and Technology
M. Russell
Affiliation:
Department of Chemistry, University of Manchester Institute of Science and Technology
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Summary

‘Blue John’ andother purple fluorites have been studied by a wide range of techniques. Hydrocarbons are not the cause of the colour of these fluorites. No significant difference in the concentrations of 73 elements between the purple and colourless zones of Blue John has been detected. The spectroscopic and thermal bleaching behaviour of the purple zones is consistent with the presence of ‘colloidal’ calcium as colouring agent, and coloration of fluorites with calcium vapour gives material showing similar properties. The distribution of colour suggests trapping of the calcium in lattice defects along {111} (cleavage) planes through {001} (growth) zones. The ‘colloids’ could be produced by aggregation of calcium atoms liberated by irradiation from sources found in the geological environment of Blue John. The banding could arise from variations in the concentration of lattice defects caused by variations in growth rates of the fluorite.

Type
Research Article
Information
Mineralogical Magazine , Volume 39 , Issue 304 , December 1973 , pp. 401 - 411
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1973

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