DERBYSHIRE HERITAGE Derbyshire Peak District - higger-tor


Fallgate quarry - Ashover Fallgate quarry - Ashover

This is Fallgate quarry at Milltown near Ashover shortly before it closed after a long working life extracting fluorspar and limestone. The fluorspar was unusual in that it fluoresced.

Fluorescence is where ultra-violet light causes fluorite crystals to glow with various colours, usually a milky blue- white. This is common in County Durham fluorite where it is apparently due to traces of rare earths in the fluorite crystal lattice. Durham fluorites contain traces of yttrium, ytterbium and europium, but these are apparently not in sufficient amounts to cause fluorescence in Derbyshire (Dunham, 1952a; Howie et al. 1982). Samples from Watersaw Rake on Longstone Edge and from Fallgate Quarry at Ashover were the only ones to fluoresce according to Bagshaw (1978). Occasionally other Derbyshire fluorites can be seen glowing faintly under strong UV light in a darkened room, though this may be due to organic compounds rather than rare earths. A variety at Castleton showed a narrow red-fluorescing band (Braithwaite et al. 1973).

In the Peak District, however, fluorite is commonly thermo-luminiscent, i.e. crystals and crushed samples glow when heated on a hot plate in a darkened room, as the lattice distortions are re-orientated and energy is released.

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