140 Washington — Suggestion for Mineral Nomenclature. 



similarity in the crystal form as shown by the system, axial 

 relations, and often cleavage. As regards the crystal system, 

 in the largest groups this similarity need not amount to iden- 

 tity, as in the feldspars, pyroxenes and am pinholes, but in gen- 

 eral the idea of a mineral group implies identity of crystal 

 system modified only in its details by the slight morpho tropic 

 changes consequent on isomorphous replacement. 



It will thus be seen that a mineral nomenclature should be 

 able to express in the name a fairly definite idea of the chemi- 

 cal composition and type of compound, as well as the crystal 

 system, and at the same time indicate the relations to other 

 minerals, and especially the membership of a mineral in its 

 particular " group." It is the object of this paper to lay stress 

 on the importance of the recognition in mineralogical classifi- 

 cation of this idea of mineral groups, distinguished by close 

 similarity in chemical composition and crystal form, and made 

 up of distinct mineral members, and to suggest a nomenclature 

 which will express these relations, based on the general princi- 

 ples of chemical nomenclature, but providing also for the 

 recognition of the crystal form as an element of the classifica- 

 tion. 



The System of Nomenclature. — As compared with the car- 

 bon compounds, minerals, and especially the silicates, present 

 very great difficulties in the study of their molecular constitu- 

 tion. This is because of their high fusing points, non-volatility, 

 insolubility, general chemical stability at ordinary or even very 

 high temperatures (so that replacements of portions of the 

 molecule are difficult), and impossibility of determination of the 

 molecular weight, assuming that the term "molecular weight" 

 is applicable to a solid body. Although we now realize the 

 importance of this branch of mineralogy, and are beginning to 

 recognize, especially among the silicates, the complex chemical 

 constitution of many minerals and the existence of certain 

 radicals or atomic groups analogous to those of organic chem- 

 istry, yet we are generally forced to be content with the expres- 

 sion of the chemical composition by simple empirical formulas. 

 The constitutional and graphic formulas of but very few min- 

 erals can be given with any degree of confidence, and in the 

 vast majority of cases we are absolutely in the dark. 



Mineralogy is essentially in the condition of organic chemis- 

 try of the early days, when the composition of alcohol could only 

 be expressed empirically as C 2 EL 6 0, that of lactic acid as C 3 H fi 3 , 

 and that of urea as CH 4 ON 2 ; whereas at present we can confi- 

 dently express them by the constitutional formulas, (C H 5 ) 

 (OH), (CH 3 ) (CHOH) (COOH), and (CO) (M 2 ) 2 , systemati- 

 cally known as ethyl alcohol, a-hydroxypropionic acid, and 

 carbonyl amide, the last differing in constitutional formula 

 from the isomeric ammonium isocyanate, (CON) (NE 4 ). 



