The Cause of Coloration in Derbyshire Blue John Banded Fluorite and Other Blue Banded Fluorites

K. J. D. Mackenzie1 and J. M. Green
Dept. of Ceramics with Refractories Technology, University of Sheffield
1Present address: Chemistry Division, D.S.I.R., Gracefield, Wellington, New Zealand.

Summary: The cause of coloration of Blue John fluorite from Castleton, Derbyshire, and blue banded fluorites from Ashover, Derbyshire, and Weardale, Co. Durham, has been investigated by a number of techniques, including mass spectrometry, optical spectroscopy, and paramagnetic resonance measurements on natural and irradiated samples. In all respects Blue John is indistinguishable from the other blue banded fluorites. Although traces of hydrocarbons were found in all the natural fluorites including Blue John, they are shown not to be the cause of the colouration. The optical spectra and bleaching behaviour are consistent with colouration by colloidal calcium rather than F-centres. The causes of colour banding are discussed.

Mineralogical Magazine; December 1971 v. 38; no. 296; p. 459-470; DOI: 10.1180/minmag.1971.038.296.08
© 1971, The Mineralogical Society
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