1873.] 



395 



[Genth. 



+ (4R,0 3 , 3 Si0 2 ) -f- 10 H 2 0, representing the product of the decomposi- 



Si0 2 : II 2 of the analyses of 



100.87 100.42 100.01 100.60 

 Particular attention was paid to the state of oxidation in which the 

 iron exists ; the ferric oxide is not due, as Prof. Leeds suggests, to a 

 superficial oxidation of some of the ferrous oxide in tlie mineral, hut is an 

 essential constituent of the chlorites, and its presence rnakes a consider- 

 able difference in the relative proportions of the protoxides and sesqui- 

 oxides. 



The oxygen ratio of RO : R 2 3 

 chlorites, above given, is as follows : 



el = 



c2 = 



c3* = 



dl = 



d2 = 



cZ3 = 



di = 



This is nearest to 7 : 6 

 formula suggested by Rammelsberg : 



4 RO, Si0 2 + 3 RO, 2 R 2 3 + 6 H 2 0. 

 All these chlorites belong to the species, which was called ripidolite by 

 G. Rose, but which is now distinguished by Dana as prochlorite. 



* Besides the printer's mistake in Prof. Leeds oxygen ratio, I have corrected it in accord- 

 ance with my views ahout the state of oxidation of the iron. 



8 : 6, which would correspond with the 



