IGO Iiitelli(jence and Miscellaneous Articles. 



fore = (RO, R2 03)2Si03 + nRO, HO, and that of the orthitea 

 = (R0. R-^03)2Si02 + nHO. 



In all epidotes, properly so called, therefore, the sum of the atoms 

 of oxygen of (RO + R'^ 0^) must be equal to the sum of the atoms of 

 oxygen of (SiO-'+ HO) ; in all orthites, on the contrary, the sum of 

 the atoms of oxygen of (RO + R-0') will be equal to the atoms of 

 oxygen of SiO'-, to which various quantities of water may then be 

 added. 



2. The vesuvians were formerly regarded as minerals possessing a 

 similar constitution to the garnets, the projjortions of oxygen in 

 RO : R- 03 : SiO'^ being in the relation of 1 : 1 : 2. The author, how- 

 ever, found another proportion, which has been confirmed by Schercr 

 and Rammelsberg. 



Rammelsberg supposes that the vesuvians are constituted accord- 

 ing to the proportions 3(RO)5 SiO^ + 2R'- O' SiO^ ; Scherer, on the 

 contrary, gives them the constitution (RO)^ (SiO^)*. 



Here also the author supposes that the bases RO and R'^ O' are 

 mutually displaced. Their fundamental molecule must be expressed, 

 just like that of the epidotes and garnets, by (RO, R^O^)-, SiO*. 

 This fundamental molecule in the vesuvians also includes small and 

 variable quantities of water. In the vesuvians, therefore, the sum 

 of the atoms of oxygen of RO +R- O^ will be equal to the number 

 of atoms of oxygen of the silicic acid combined therewith, to which 

 also various quantities of water may be added. The general formula 

 of the vesuvians would consequently be (RO, R* 03)biO''-|-nHO. 



3. The garnets contain RO, R'^ O^ and SiO-, usually in a propor- 

 tion in which the oxygen corresponds with the numbers 1:1:2. 

 In the garnets, indeed, the proportion of oxygen of RO : R- O^ : SiO- 

 is subject to variation. In all cases, however, the sum of the atoms 

 of oxygen of RO -f R- O^ is equal to the atoms of oxygen of SiO^. 

 The garnets consequently have the same fundamental molecule as 

 the epidotes and vesuvians, namely (RO, II" O^) SiO^, and are there- 

 fore, as they also contain the same chemical constituents as those 

 minerals, polymorphic with them. In individual cases the variations 

 of RO : R' 0^ go so far that R- O^ is completely displaced. The 

 minerals which, according to the author, belong here are the fol- 

 lowing : — 



Garnet group = (RO, R2 O^)"- SiO^. 



1. Garnet = (RO, R^ Qs)'^ SiO"-. 



2. Sodalite = 6(R0, R^O^)"- SiO'^-fNaCl. 



3. Hauyne = 3(R0, R* Os)^ SiO^ + CaO SO^. 



4. Nosean = 6(R0, R^O^)"- SiO' + NaO SO^. 



5. Ittncrite = (RO, R'^ O')"- SiO'2 + n(NaO SO^). 



6. Helvine = 3(110*) SiO« + Mn. 



— Journ.filr Prakt. Chemie, vol. Ixx, p. 321. 



