Author:
Braithwaite R. S. W.,Flowers W. T.,Haszeldine R. N.,Russell M.
Abstract
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.
Subject
Geochemistry and Petrology
Cited by
26 articles.
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