Published online by Cambridge University Press: 14 March 2018
I obtained this summer a most beautiful variety of fluor spar, which was raised from the 145 fathom level of the Holmbush Mine. It is of a transparent azure-blue colour, and shows well marked fluorescent phenomena, though not so strongly as that of Weardale, Cumberland.
Some of the specimens are deep blue in one part and limpid like glass in another ; it was found that while the deeply coloured part was strongly fluorescent the limpid part had little or no effect upon the refrangibility of the light passed through it.