234 PAIGE AND steiger: sericitization 



are the metals of positive valence, to the left the nonmetals of 

 negative valence, etc. ' 



The table suggests that the elements in the first two series are 

 systems too simple to have the more complicated relationships 

 fully developed. It is interesting, however, to note in this con- 

 nection the possibility of two forms of neon, perhaps an embry- 

 onic foreshadowing of the first triplet Fe, Co, Ni. But the main 

 use of the periodic table is to assist the mind in grasping the host 

 of experimental facts accumulated by the chemist. Today these 

 facts are of interest to a wider circle of scientists and the slightest 

 simplification in their presentation is welcome. 



REFERENCES 



Chancourtois, B. de, Nature 41: 186. 1889 (by P. J. Hartog). 



Harkins, W. D., and Hall, R. E., Journ. Amer. Chem. Soc. 38: 169-221. 1916. 



Mendeleef, D., Chem. News. 40, 1879; 41, 1880; Principles of Chemistry, Vol. 



2. 1891. 

 Newlands, J. A. R., Chem. News. 10: 94. 1864; 12: 83, 94. 1865. 

 Stoney, G. J., Proc. Roy. Soc. 85: 471-473. 1911 (by Lord Rayleigh). 



GEOCHEMISTRY. — Fluorine in sericitization.^ Sidney Paige 

 and George Steiger, Geological Survey. 



The intense alteration of granodiorite or quartz monzonite 

 porphyries in which large deposits of secondary chalcocite occur 

 (the so-called porphyry coppers) is a matter of common knowl- 

 edge. This alteration, of two kinds — primary, resulting in the 

 introduction of sericite, pyrite, and quartz; and secondary, 

 resulting in the deposition of chalcocite from descending sulphate 

 solution — leaves the original rock in a scarcely recognizable 

 condition. 



The degree of sericitization is in many places astonishing. 

 Where fractures are numerous and ascending waters have freely 

 circulated, the rock mass may be almost wholly replaced by 

 sericite, quartz, and pyrite, the former two minerals occurring in 

 about equal amounts. 



Changes resulting from the descending, oxidizing waters have 

 been in places quite as noteworthy; the sericitized rock has been 



* Published with the permission of the Director of the U. S. Geological Survey. 

 Mr. Steiger is responsible for the chemical analyses. 



