lower levels. An interesting case is that of the Fluor Spar occurring in geodes at Gourock in Scotland.
The
associated minerals include most of those found in mineral veins, the
commonest being Galena, Quartz, Chalcopyrites, Barytes, Calcite, etc.
Its
chemical composition is fluoride of calcium Ca F,. Chlorine is
sometimes present in traces, and the colouring matter is usually
considered to be a compound of carbon and hydrogen. Enclosures of
minute grains of Quartz are sometimes seen, and the blue shades with a
greasy lustre are most prone to contain bubbles of liquid.
Its
distribution is so wide that only the more important localities can be
indicated. In England one of the best localities is the district of
Alston Moor, comprising the great upland tract to the east of
Cross-fell. Here on the old " Corpse-road " from Garrigill to Kirkland,
Fluor Spar from the adjacent lead mines has been used as road metal;
and to one who is fortunate enough to be passing over it when the sun
comes out after a shower, the sparkle of colour is not likely to be
forgotten. From the mines of Weardale beautiful violet crystals are
obtained. Others, of a green colour by transmitted light, show the
property of fluorescence in a marked degree, turning to a blue when
viewed by reflected light. Fine honey-yellow crystals occur at
Scordale, in Westmorland. Derbyshire is famous for the massive variety
known as " Blue John," from which vases and many ornamental objects are
made. This variety is particularly fine from Tray Cliff, near
Castleton. CornÂwall and Devonshire produce crystals having a wide
range of colour. Huel Mary Ann, in Cornwall, is noted for the beautiful
blue crystals; also Huel Trelawney. St. Agnes
