Washington — Suggestion for Mineral Nomenclature. 141 



Indeed, the theory of mineral constitution at present is in 

 many ways analogous to the "theory of types" in organic 

 chemistry, formulated by Gerhardt about 1850, as is seen in 

 the general reference of the silicate minerals to simple silicic 

 acids, H 2 Si0 3 , H 4 Si0 4 , H 2 Si 3 7 , etc. Kekule's " theory of linked 

 atoms " has now superseded this in organic chemistry, * and 

 the applicability of this to mineral chemistry has only recently 

 begun to be realized. 



The study of the molecular constitution of minerals and 

 attempts at the establishment of constitutional formulas have 

 been undertaken by Tschermak, Groth, Clarke, and many others, 

 either through direct experiment or study of alteration pro- 

 ducts, but so far with doubtful success in most cases, and it 

 will probably be many years before mineralogy attains to the 

 knowledge requisite for formulas like those of modern organic 

 chemistry. 



In three important papers Penfieldf established the complex 

 character of the acidic portion of the tourmalines and amphi- 

 boles, and showed the effect of the mass action of the complex 

 acid in controlling crystallization, allowing replacement of the 

 hydrogen atoms of the hypothetical acid by very different ele- 

 ments or radicals, and with different valences, but without 

 change in crystal form. He also speaks of these acids as tour- 

 maline acid and amphibole acid, with the implication that an 

 essential character of their salts is adherence to the particular 

 crystal form of tourmaline and amphibole respectively. 



More recently the problem of the constitution of some sili- 

 cates has been studied by Tschermak, Baschieri and others.:); 

 These investigators have identified certain silicic acids, which 

 they call after the mineral names, among them being: anorthi- 

 tic acid (H 2 Si0 3 ) albitic acid (H 2 Si 3 7 ), leucitic acid (H 4 Si 2 6 ), 

 heulanditic acid (H 10 Si 6 O 17 ), granatic acid (H 4 Si 3 8 and dato- 

 litic acid (H 2 Si 2 5 ). Their method, it may be remarked, does 

 not apparently permit of discrimination between a purely sili- 

 cic or an alumo- or boro-silicic acid, and none of these workers 

 suggests, like Penfield, that the acid or the acid name implies 

 the crystal form of its salts. 



It is suggested here that this concept of Penfield of silicate 

 minerals as salts of mineral acids, in many cases of much 

 greater complexity than is implied by the empirical formula, 

 with the implication of the adherence of the salts to a charac- 



* Cf . C. Schorlemmer, Rise and Development of Organic Chemistry, Lon- 

 don, 1894, pp. 39, 69, and 155. 



f This Journal, vii, p. 97, 1899: x, p. 19, 1900; xxiii, p. 23, 1907. 



i Tschermak, Sb. Ak. Wiss. Wien, cxii (1), p. 355, 1905, cxiv(l), p. 455, 

 1905, cxv (1), p. 217, 1906. E. Baschieri, Proc. verb. Soc. Tosc, xvi, p. 34, 

 1907; Atti Soc. Tosc. Mem., xxiv, p. 133, 1908. Himmelbauer, Sb. Ak. 

 Wiss. Wien, cxv(l), p. 1184, 1906. 



