Prof. Chapman on the Classification of Minerals. 177 



derived from a full recognition of isomorphism, to avoid the 

 most striking incongruities. A few examples will be sufficient 

 to establish this assertion: — (1.) Silver, arsenic and sulphur, as 

 " simple substances/" must be placed in one and the same group. 

 It is very evident, however, that silver has a far greater affinity 

 to the argyrose or sulphide of silver, in every point of view, than to 

 either sulphur or arsenic. What, moreover, has sulphur in com- 

 mon with these other " simple substances " that we should place 

 it with them ? — and thus separate it more or less widely from orpi- 

 ment, a mineral to which it is allied not only by general physical 

 characters and crystallization, but also by the kindred conditions 

 under which both occur in nature. (2.) Iron pyrites and 

 molybdenite are bisulphides, and, as such, fall into the same 

 chemical division; all natural analogies are, however, against 

 this union, and in favour of the grouping of molydenite with 

 many of the simple sulphides. (3.) Cinnabar belongs chemically 

 to these latter, but crystallographically and physically it has little 

 affinity with them. It is closely allied, on the other hand, 

 through xanthocone, to the ruby silvers, from which, in a che- 

 mical point of view, it should be altogether removed. (4.) The 

 usually adopted chemical group of " oxides " includes a consi- 

 derable number of minerals, which appear to have little or no 

 natural connexion with one another. Red zinc ore, corundum, 

 magnetic iron ore, cassiterite, and minium, for instance, can 

 scarcely be said to have two characters of any importance in 

 common ; and yet, with many other equally opposite substances, 

 the chemical classification places them together, and, indeed, 

 almost side by side. 



It seems hopeless, therefore, in the present state of chemical 

 theory to attempt to found a successful mineral classification on 

 chemical grounds alone ; and although a perfectly satisfactory 

 distribution of minerals may at present be unattainable by any 

 method, yet it can only be by the employment of every character 

 capable of shedding light on the true nature of minerals and 

 their mutual relations and affinities, that we can ever hope to 

 accomplish this desirable end. The greater the number of 

 physico-chemical classifications, the greater the ultimate chance 

 of success : each attempt yielding its quota towards the end in 

 view, and striking out perhaps some new idea for future elabora- 

 tion. Even utterly unworthy classifications of this kind have 

 their negative merit, in setting before us in a more palpable 

 light the errors which are especially to be avoided. Without 

 further apology, therefore, I will briefly point out the general 

 features of a system which appears to me to fulfil the two-fold 

 object of discrimination and natural grouping as effectually as this 

 object can be fulfilled by any single classification. That some 



Phil. Mag. S. 4. Vol. 6. No. 38. Sept 1853. N 



