showing, at the same time, the results obtained, some years ago, by M. 

 Moberg, in the analysis of some emeralds from Finland : — 



Emeralds from Mexico (M. Lewy). Emeralds from Finland (M. Moberg). 



Silica . . . 67-9 67-359 



Alumina . . 17-9 lC-465 



Glucina . . 12-4 12-747 



Magnesia . . 0*9 — 



Oxide of iron — 1-49 



Soda ... 0-7 ....... . — 



Titanic acid . traces 0-28 



Both these analyses show that the emerald contains 1 atom of alumina, 

 1 atom of glucina, and four atoms of silica. In that of M. Lewy 

 slight traces of chromic oxide were weighed with the magnesia, and 

 probably some titanic acid with the alumina. The green colour of the 

 emerald is darker in those specimens which furnish to analysis most 

 organic matter ; it is completely destroyed by heat, the stone becoming 

 white and opaque. 



On the communication of these results to the Academy, M. 

 Bousingault observed that he also, in former days, had visited the 

 Muso mine, and that he had picked out of the strata in which the 

 emeralds are found, pieces of gypsum of a beautiful green colour, 

 resembling that of the emerald. He had no doubt, from M. Lewy's 

 observations, that the green colouring with which the gypsum was 

 impregnated was identical with that just discovered by M. Lewy in 

 emeralds. 



M. Daubree has furnished us with some new and interesting details 

 concerning the artificial production of minerals. By a close observation 

 of the methods employed by nature, and a certain intrepidity in the 

 laboratory, this enthusiastic geologist has had the good fortune to 

 produce some crystallized specimens of minerals which have never before 

 been purposely formed or accidentally found in scoriae. He formerly 

 observed in the mineral springs at Plombieres, the waters of which 

 contain silicate of potash and soda, and have a temperature of + 70*^ 

 Centigrade, the formation of certain well-known silicates and other 

 minerals usually found in the veins of eruptive or primitive rocks. 

 Most of these have been formed, since the time of the Romans, in the 

 orifices of the mineral springs in question. An old Roman tap in 

 bronze was found covered with a crust of sulphide of copper which, 



