Manchester Memoirs, Vol. Ixii. (1918), No. 10. 11 



Tourmaline. — Though this is quite a common mineral, yet clear 

 crystals are rare, and generally valuable, especially the lighter coloured 

 ones. Three specimens were used, a dark green semi-transparent 

 crystal from Cornwall, a pink crystal (rubellite) from Canada, and 

 a small colourless specimen from Elba. 



The green specimen became darker and more opaque on heating, 

 and no visible effect was produced by radium on the heated or 

 unheated specimens. 



The pink crystal turned quite white and opaque on heating 

 before the blow-pipe. Radium produced little visible effect on the 

 original specimen (slight darkening of the pink colour), and none 

 at all on the heated specimen. Cathode rays produced no colour 

 effect on either, but the heated specimen showed a very fine orange 

 glow, whilst the unheated crystal was unaffected. 



The colourless specimen showed a faint pink colour after one 

 day under 50 mg. of radium, and this was considerably strengthened 

 after four days' further treatment. Its colour then showed con- 

 siderable resemblance to that of the Canadian rubellite, and five 

 days' further treatment with radium did not change this. The limit 

 of colour for this specimen had thus apparently been reached. 



Topaz. — Transparent crystals of topaz are common, and are 

 found colourless, yellow, pink and blue, but are usually intersected 

 with large numbers of flaws. 



Yellow topaz from Brazil changes to a purplish pink on strongly 

 heating, while similarly coloured specimens from Aberystwith become 

 almost colourless. 



None of these exhibit any thermo-luminescence before, and 

 very little after, radium treatment. A clear colourless crystal from 

 the Mourne Mountains acquired a fine deep yellow colour after four 

 days under the action of 10 mg. of radium. 



A yellow crystal from Brazil became slightly deeper coloured 

 after similar treatment. 



A similar crystal, heated until it turned pink, and then treated 

 with radium, regained its original colour and then became slightly 

 deeper coloured than the unheated specimen. On reheating, the 

 crystal again became pink, with slight thermo-luminescence. 



Zircon. — Clear crystals occur as hyacinth (pink to deep red) 

 and jargoon (colourless). 



Specimens of hyacinth from Tasmania and from the centre 

 of France were used. These varied greatly in their behaviour on 

 heating. Some of the Tasmanian specimens became nearly colour- 

 less when heated in a hard glass tube and quite colourless and 

 transparent when heated on platinum wire in a bunsen flame. On 

 the other hand, some of the French specimens still retained a pale 

 yellow colour after five minutes' heating in a good blow-pipe flame. 



All the specimens, heated or unheated, showed a greenish glow 

 when exposed to radium. The unheated ones were unchanged in 

 colour, but the heated ones all regained their colour to a greater 

 or less extent. 



The colour of those Tasmanian specimens which had been 



