8 Newbery- — Lupton, Radio-activity and Coloration of Minerals. 



" rotting " action was observed with the crystalline specimens used 

 in the present work, so that this appears to be a property of fused 

 quartz only. 



With all the specimens the action was very slow. A clear 

 limpid crystal on treatment with 25 mg. of radium for seven days 

 became smoky, the colour being strongest at the spot where the 

 radium tube was in contact with the crystal, but penetrating to a 

 depth of 1 cm. into the crystal. 



Rose quartz after decolourising by heat also became smoky, 

 but rather more readily than the rock crystal. The pink colour 

 was also restored to a slight degree. Amethyst decolourised by 

 heat showed little or no smokiness on treatment with radium, but 

 the clear purple colour was slowly restored. 



A nearly black cairngorm, which was easily rendered clear and 

 colourless by heat, slowly regained its colour under the action of 

 radium, the change being rather more rapid than with any of the 

 other quartz specimens. 



All the crystals thus recoloured were readily decolourised by 

 moderate heat, and in all cases a very faint thermo-luminescence 

 was observed. 



Ruby. — A small light-coloured fragment from Carolina on 

 heating strongly appeared green, but regained its original colour 

 on cooling. Treatment with 25 mg. of radium for ten days had 

 no appreciable effect on the colour, but a slight thermo-luminescence 

 was produced which rapidly disappeared on further heating. Other- 

 wise, no change was observed. In view of the fact that artificial 

 rubies, indistinguishable from natural ones, can be made by fusing 

 pure alumina with a trace of chromium, the unchangeability of the 

 colour by radium is not surprising, the colour being intrinsic and 

 not exotic. 



Selenite. — A number of clear and perfect crystals from the 

 Kimmeridge clay were used. These decompose with loss of water 

 of crystallisation at a comparatively low temperature, so that no 

 thermo-luminescence could be observed. 



After the application of 50 mg. of radium for two days, a 

 peculiar effect was observed in the crystal. On looking through 

 the two large faces of the crystal at a white object, these faces 

 appeared to be divided into four triangles by diagonals of the 

 parallelograms. The two triangles having as bases the longer sides 

 of the parallelogram were coloured a faint smoky brown, while the 

 other two were unaltered. Further exposure to 25 mg. of radium 

 for fourteen days darkened the coloured parts slightly, but left the 

 remainder of the crystal still unchanged. Several crystals were 

 tried and fresh clear faces prepared by cleaving off thin sections ; 

 also the direction of the radium tube relative to the crystals was 

 changed, but the same result was obtained in every case. The 

 explanation of this peculiarity is due to Sir Henry Miers. 



When the crystal was in its initial stages of growth, its faces 

 were similar, and similarly situated, to those of the fully developed 

 crystal. Certain of these faces have different properties from other 



