Manchester Memoirs, Vol. Ixii. (1918), No. 10. 



X. Radio-activity and the Coloration of Minerals. 



By Edgar Newbery, D.Sc, and Hartley Lupton, B.Sc. 



(Communicated by J. Wilfrid Jackson, F.G.S.) 

 (Read April 23rd, 1918. Received for publication June yd, 1918.) 



The occurrence of the most varied and beautiful exotic colours 

 in certain minerals is a feature whith attracts the attention of the 

 most casual observer in a mineral museum. 



Many attempts have been made to explain the source of these 

 colours, but it is remarkable that no explanation so far offered has 

 met with general acceptance. It is well known that certain in- 

 organic or mineral substances acquire strong colours under the 

 influence of the radiations from radium or in a cathode-ray tube, 

 and the occurrence of radium or other radio-active bodies in the 

 earth has been shown to be so widespread that it is difficult to 

 obtain a sample of rock which does not show some traces of this 

 activity. 



The present work was undertaken, therefore, in order to deter- 

 mine, if possible, how far the presence of radio-active substances must 

 be taken into account when trying to solve the question of the source 

 of these exotic colours. 



Previous Work. — -So much work has been already done on this 

 subject that it is impossible in a paper of this type to give more than 

 the briefest outline of those papers which deal most directly with 

 the same minerals as those used in the present work. Many state- 

 ments have been made which apparently contradict each other, but 

 which may both be true for the particular specimens used by each 

 worker. It should therefore be emphasised that whilst the observa- 

 tions described here could be repeated with certainty as often as 

 desired with the specimens used, other specimens apparently iden- 

 tical, and even from the same locality, may fail entirely to exhibit 

 similar phenomena. An alphabetical list of references is given at 

 the end of this paper. 



Wyrouboff studied the colours of natural fluor-spar and came 

 to the conclusion that they are due to the presence of two hydro- 

 carbons, one producing blue and the other red colours. Assuming 

 the former to be the more volatile, he explains the change from blue 

 or violet to purple which is observed on moderately heating certain 

 fluor-spars. 



This explanation is untenable in the light of Berthelot's experi- 

 ments, since certain decolourised fluors had their original colour 

 completely restored by prolonged exposure to radium. If the 



