20 FROM AN EASY CHAIR 



corundum ; green and yellow " sapphires " are also 

 common. The Oriental ruby is similarly only red, 

 transparent corundum like it only oxide of aluminium 

 or alumina. 



Diamonds are pure crystalline transparent carbon. 

 Commonly they are colourless and transparent, but are 

 sometimes black or white and opaque. Transparent 

 diamonds are often found of a straw colour, rarely 

 of a deep blue (the Hope Diamond), more rarely 

 green (the Dresden Diamond), and rarest of all 

 red. 



If radium were really able (as some people have 

 wrongly inferred from the French experiments) to 

 change the chemical nature of corundum and convert 

 it into topaz and emerald, the case would be very 

 different from that of merely changing the colour of 

 the corundum. What is to-day called " topaz " is a 

 sherry-yellow crystal consisting of silicate of alumina 

 and of fluoride of alumina. It turns pink when heated, 

 and is also known of a blue colour and colourless. The 

 topaz of the ancients from .the coasts of the Red Sea 

 is of a different chemical nature, and is now called 

 peridote. Yellow corundum is sometimes wrongly called 

 Oriental topaz, and the yellow-brown quartz crystals 

 properly known as cairngorms are sometimes wrongly 

 called Scotch topaz. So that the word " topaz " is used 

 loosely as well as strictly, and confusion results. Emerald 

 is widely distinct from corundum, sapphire, and ruby. 

 It is a silicate of alumina and beryllium, and in its 

 coarse and pale-coloured variety is known as beryl. 



From all this it appears that some names of precious 

 stones indicate substances quite distinct from one 

 another chemically, built of differing elements, and also 

 per contra that what is actually one and the same kind 

 of precious stone in chemical composition and native 

 crystalline form may present examples possessing various 

 colours and degrees of transparency, each variety being 



