Classification of Natural Silicates. 135 



The Persilicates are arranged in like manner in five group.*, 

 the received ratios of silica and the fixed bases being given, aa 

 before, in a column to the left. The adamantoid persilicates 

 include dumortierite, andalusite, fibrolite, topaz, cyanite, bu- 

 cholzite, the zircons and anthosiderite. The phylloids include 

 pholerite, kaolinite and pyrophvllite ; and the argilloids, the 

 various amorphous hydrous silicates of alumina from the highly 

 basic schrotterite, through halloysite, to the more silicious cimo- 

 lite and smectite. 



The relations of fluorine in silicates like topaz and chondmdite, 

 of chlorine in pyrosmalite, sodalite and scapolites, and of sulphur 

 in helvite, lapis-lazuli and danalite are considered at length by 

 the author. Tables showing the values of P and V, together 

 with the simplest atomic formulas deduced from chemical analysis 

 are given for most well-known silicates. The discussion of the 

 equivalent weights of these species, and of their defi lite place in 

 a chemical classification of polysilicates is noticed, but is left for 

 future consideration. 



If we regard the silicates as constituting a natural order, 

 the three groups already noticed may be called sub-orders ; 

 A. Protosilicates ; B. Protopersilicates ; C. Persilicates. The 

 divisions of these will constitute tribes, and the tribal characters 

 being repeated in the sub-orders, we distinguish the spathoids, 

 adamantoids and phylloids, by prefixing the distinctive syllables 

 of the sub-orders; as protospathoid, peradamantoid and protoper- 

 phylloid. The sub-divisions of these tribes into families, genera 

 and species cannot here be discussed. The genus feldspar, 

 including anorthite, albite and perhaps iolite, with other genera, 

 some of which are represented respectively by orthoclase, by 

 leucite, and by sodalite, will constitute the family of the feld- 

 spathides. The families of the micas and the pyroxenides in 

 like manner will each include several genera, having different 

 values for V. 



The application of the principles above defined to carbonates, 

 and the reference of the various carbon-spars to different polycar- 

 bonates, were long ago shown by the author in his papers already 

 noticed. The extension of like views to all liquid and solid inorganic 

 species, both natural and artificial, is but a matter of detail and 

 labor, and when fully carried out will be the basis of a new 

 chemistry. 



