L. V. Pirsson — Classification of Igneous Rocks. 281 



alumina into feldspar, and a feldspathoid (lenad) 



appears ; this increases with lowering silica until no 

 feldspar is present. 



The quantitative relation of the ferromagnesian 



CLASSIFICATION OF IGNEOUS ROCKS. 



c 



SODACALCIC FeLDSPAES 



D 

 Calcisodic Feldspars 



E 

 No Feldspar 



5 



Felsic 



Mafic 



7 

 Felsic 



8 

 Mafic 



9 

 Mafic 



Quartz 



Di6rite 





Quartz 



Gabbro 







Qtz. Dior. Porjj'y 





























14 15 

 Diorite 



Diorite Porphyry 



Kersantite 

 Andesite 



16 17 

 Anorthosite 

 Gabbro and Norite Group 



Diabase 



Basalt and Melaphyre 



18 



Peridotite 



Group 



Hornblendite 



Pyroxenite 



Picrite and 

 Augitite 



23 

 Theralite 



(in part) 



24 

 Essexite 



(in part) 



25 

 Rouvillite 



20 

 Teschenite 



27 



Jacupirangite 



Yamaskite 





Basanites 



Limburgite 



32 



33 



34 



35 



36 





























• 





\ 



{mafic) minerals to the quartz, feldspars, and feldspa- 

 thoids {felsic minerals) in the A, B, C, D divisions is 

 expressed under a felsic and mafic column in each. In 

 one, felsic minerals dominate and form 50-100 per cent of 

 the rock; in the mafic, the ferromagnesian ones dominate 

 in like manner. Other quantitative relations, like those 

 affecting the felsic minerals among themselves, will be 

 discussed later in appropriate places. 



