52 Mr. F. Field on a Variety of the Mineral Cronstedite. 



Such is the brief account of our researches which we wished 

 to present to-day to the Academy. It is probable that our 

 experiments, which give, in considerable masses, substances 

 whose hardness is comparable to that of the natural ruby, will 

 be utilized from time to time by the watchmaker, and even by 

 the jeweller. We will say, in conclusion, that in this labour 

 the aim we pursue is exclusively scientific ; consequently we 

 put into the possession of the public the facts we have dis- 

 covered, and shall be very happy to learn that they have found 

 useful industrial applications. 



VIII. OnaVariety of the Mineral Cronstedite. By Frederick 

 Field, F.R.S., Vice-President of the Chemical Society*. 



THE various analyses of the interesting mineral Cronstedite, 

 named after the Swedish mineralogist Cronstedt and 

 hitherto found only in two localities (Przibram in Bohemia and 

 -Wheal Maudlin in Cornwall), are rather conflicting, since the 

 amounts of ferrous and ferric oxide differ considerably, as the 

 following results will show. Nevertheless all examinations 

 tend to prove that Cronstedite is essentially a hydrous silicate 

 of ferrous and ferric oxide. 



From four specimens from Przibram we have: — 



Silicic acid 22*452 



Ferric oxide 



Ferrous oxide 58*85.2 



Manganous oxide 5*078 



Magnesium oxide 2*885 



Water 10*700 



99*967 



This was corrected by Yon Kobell, after a determination of 

 the degree of the oxidation of the iron, which gave: — 



Silicic acid 22*452 



Ferric oxide 35*350 



Ferrous oxide 27*112 



Manganous oxide 5*078 



Mangnesium oxide 2*885 



Water 10*700 



103*577 



And in two more analyses, one by Steinmann and one by 

 Damour, the ferrous oxide varied more than 2 per cent.: — 



* Communicated by the Author. 



