66 
THE GEOLOGIST. 
stowed away with the greatest care for a few days. As to tlie 
cause of this hardening of stones recently extracted from their natural 
beds we shall have occasion of referring to it presently. 
M. Lewy has shown also in his interesting paper {Researches on the 
Formation and Composition of Emeralds),'^- that the beautiful green 
colour, so much admired in the stones of which we are speaking, 
and without which they would, in all probability, be valueless, is owed 
to an organic substance somewhat similar to that called chlorophylle, 
which colours the leaves of plants, f The green colour of emeralds 
has always been attributed to a slight quantity of chromic oxide, which, 
although it certainly does play an important part in the coloration of 
other minerals, has positively nothing to do with that of emeralds. 
Analysis has furnished only an exceedingly slight quantity of chromic 
oxide ; so small, indeed, that the distinguished chemist whose work we 
are analysing could not weigh it separately. Our readers have, perhaps, 
heard of, or seen, a mineral called ouwarovite, a sort of chromiferous 
garnet, whose green colour (which withstands heat, whilst that of the 
emerald does not) is exactly that of the emerald ; but ouwarovite 
furnishes 23 and-a-half per cent, of oxide of chrome, whereas in 
emeralds, as we have seen, there is only a sUght vestige of this 
green oxide. This is certainly a new and unexpected result. 
A certain number of facts related in his memoir lead M. Lewy to 
aflBrm that emeralds have been deposited from water. It would, perhaps 
be more rational to say that water has been active in their production % 
— First, besides the organic colouring matter, emeralds contain about 
2 oer cent, of water. In the next place, the black white-veined lime- 
stone in which they are found contains fossil ammonites. This lime- 
stone, perfectly freed from the microscopic emeralds with which it is 
strewed, by digestion with dilute hydrochloric acid, gives in analysis a 
T u o 0 o th part of glucina. 
Great uncertainty has prevailed as to the mineral constituents of the 
emerald and its true chemical formula ; this has determined me to give 
here the numbers obtained by M. Lewy, and to corroborate them by 
• Presented to the Academy of Sciences, Nov. 15th, 1857. 
t It is, perhaps, as well to observe that M. Lewy has not ascertained if this 
organic substance in the emerald contains oxygen or not. He seems to consider 
it as a carburet of hydrogen. 
% See fui ther, the phenomena recently observed by M. Daubree. 
