Review of Dana's Mineralogy. 375 



well understood, it is not too much to assert, that the chemical and natu- 

 ral systems will be identical. 



"In the received chemical systems, analogies and affinities are very 

 generally violated. Some authors arrange minerals according to the elec- 

 tro-positive element (the base) in their composition ; and others follow 

 the electro-negative element, (the acid:) and in both cases numerous 

 difficulties obtain. The true system should conform to the one or the oth- 

 er, according to which is the characterizing ingredient; and on this plan, 

 keeping in view also the principles of isomorphism, the chemical class- 

 ification would not differ from the natural system. 



"Carbonate of lime, carbonate of magnesia, carbonate of iron, and 

 carbonate of manganese, are allied chemically — for their bases, lime, 

 magnesia, oxyd of iron, and manganese, are isomorphous — and in phys- 

 ical and crystallographic characters they are also very similar. The 

 group is therefore a natural one. The sulphates of several of the met- 

 als constitute a family of vitriols which are always associated in com- 

 mon language, and with equal propriety in science. But most chemical 

 arrangements break up these natural groups, and place sulphate of iron 

 (green vitriol) and carbonate of iron together under iron, sulphate of 

 copper (blue vitriol) under copper, and so on. There is a natural group 

 of alums, a potash-alum, soda-alum, magnesia-alum, &c, which is al- 

 most invariably broken up in the chemical systems, one placed with the 

 salts of potash, another with the salts of soda, &c. A single species in 

 mineralogy, pyroxene, is sometimes subdivided and distributed in vari- 

 ous parts of the system. This species includes several distinct chemi- 

 cal compounds, as will be seen by referring to Pyroxene, in the descrip- 

 tive part of the treatise ; but they are so closely related physically, and, 

 if we consider the isomorphism of the bases, we may say chemically 

 also, that many chemists rank them in the same family. The micas ev- 

 idently form a natural group, yet a chemist separates the rose mica from 

 the others, and places it with other lithia minerals, because it contains a 

 few per cent, of lithia. The natural family of the feldspars and the 

 zeolites are usually broken up in the same manner. A few per cent, of 

 the base will often lead to a dissevering of the closest affinities. The 

 sulphurets of iron, copper, &c. form evidently a natural group chemical- 

 ly as well as mineralogically, yet, without reference to their relations, 

 they are usually distributed under the different metals, although sulphur 

 is here the characterizing ingredient. All the compounds of the metals 

 are generally thrown together ; whereas even chemistry, if its princi- 

 ples are well considered, would suggest that the salts of the various met- 

 als are in general more nearly allied than the salts and oxyds of the 

 same metal. There can be no more unnatural association of species 

 than the sulphate of iron, (green vitriol,) carbonate of iron, phosphate 



