Dr. J. E. Reynolds on certain Mineral Silicates. 289 



Basic or Subsilicates. 



Class 1. Chondroditc. . . Mg" 8 X°* 



/O c \ 



= Mg' /8 2 ||0 12 ||Si 3 (Dana). 



\Si> 



Class 2. Gehlenite . . (iR e -HB) 3 X° a 



/0«\ 



\ Si / 



Andalusite. . . . Ai :i Vb n 



/o 6 \ 



\Si/ 

 Topaz .... 4i3V(^Fi2 + | ) 



/o 6 \ 



\Si/ 

 Euclase aH d 4-§Be //3 4-fAi 3 )\<V 

 /0 6 \ 



Probably the composition of datholite and tourmaline can 

 be also best exhibited on a similar plan, if we regard the boric 

 anhydride as a basic constituent. It need scarcely be said that 

 this is a very doubtful point. 



\Si/ 

 Class 3. Staurolite . . (H^R'^^Yo 1 - 



/0 G \ 



It will have been already noticed that I have rarely dealt with 

 the formulae of hydrous metallic silicates. So little is really 

 known of the function of the water contained in them, that it 

 seemed undesirable to dwell upon their atomic formulae at pre- 

 sent ; at the same time it is necessary to say that the composition 

 of large numbers of them can be easily represented in accordance 

 with the plan proposed in this paper. This is especially the 

 case with the interesting family of the zeolites, the relations of 

 which to that of the felspars can be then clearly traced. 



In the preceding pages I have done little more than note down 

 the main points which I sought to give prominence to. In every 

 section numerous cases occur which admit of extended treatment, 

 yet these have not been dwelt upon, nor have more formulae been 

 given than were absolutely necessary to facilitate explanation. 

 This course seemed preferable, as it then became possible to give 

 an outline of the subject without extending this paper beyond 

 due limits. 



In conclusion, I may sum up the main points of this paper 

 Phil. Mag. S. 4. Vol. 36. No. 243. Oct. 18G8. U 



