271 



No. 13. Dark, alkali-feldspar- or rhombenporphyry, Pine Hill Area, West 

 Quincy, Ma.ss., Analyst, C. H. Warren. 



In the parallel column is an analysis, by G. Forsberg, of a rhom- 

 benporphyry from Slotsberg n. Tonsberg, Norway (W. C. Brogger, 

 Z. K., XVI, p. 35, 1890). 



The norm of the "Quantitative" Classification is as follows: 



Quartz 4.44 



Orthoclase 31.14 

 Albite 38.25 



Anorthite 7 . 23 

 Diopside .99 



Hypersthene 7.86 

 Magnetite 3 . 25 

 Ilmenite 1 . 67 



Apatite 3 . 36 



96TT9 



#el5 = 3<T>|. Class 11. 

 81.06 Salic Minerals. 



T 1 



Q = .05 < 7; Order 5: perfelic. 



Q^Q^' = 4. 9 ; Range 2 ; domalkalic. 

 > 17. 13 Femic Minerals. 



j^~Q = .76. Subrange 3; sodipotassic; Mon- 



zonose. 



It is impossible to calculate, other than approximately, the mineral 

 composition both on account of the altered character of the rock, and 

 the uncertainties as to the exact composition of the various minerals, 

 nor did it appear, in order to help out the situation, advisable to 

 attempt to separate the feldspar and analyze it on account of the 

 included pyroxene and secondary minerals. The approximate mineral 

 composition (to 100%) of the rock has been calculated as follows: — 



