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



this age distinction was laid aside. The groups of plu- 

 tonic and effusive rocks thus formed on a geologic basis 

 were subdivided according to their mineral composition 

 on the same general lines as in the preceding classifica- 

 tion. Texture in them is not used as a means of classi- 

 fication, except in so far that certain textures are held 

 to accompany each group and to be characteristic of 

 them; that is, the abyssal rocks are granular and the 

 effusives are porphyritic. The dike rocks are subdivided 



^ 



Table No. 2, 



EOSENBUSCH CliARSIFICATlON OF 



Igneous Eocks 





Characterized 

 by 



Plutonic 



Group 



Granular 



Group of Dike Rocks 

 Porpliyritic and Panidiomorphic. 



Volcanic Group 

 Porpliyritic. 





Granite 



Granite-porph'ritic 



Aplitic 



Lamprophyric 



Quartz- 

 porphyry 

 Rhyolite 



Alkalic I +'3'^- 

 feldsp's j _Qj^ 



Granite- 

 porphyry 



Aplite 





Syenite 



Syen.-porph'y 



Bostonite 



Minette 

 Vogesite 



Orthophyre 

 Trachyte 



Alk. Feldspars 



and Nephelite, 



or Leucite 



Nephelite- 



Syenite 

 Leuc.Syen. 



Neph. Syenite- 

 porphyry 

 Leu.Syen.por'y 



Tinguaite 

 Leuc. Ting. 





Phonolite 

 Leucitophyre 



Feldspathoids 

 Nephe- +01iv. 

 lite — Oliv. 



Bekinkinite 



Ijolite 

 Missourite 

 Fergusite 









Neph. Basalt 









Nephelinite 



T .^ -}-01iv. 

 Leucite j- _qj.^_ 



Melilite 









Leucite-Basalt 









Leucitite 







AInoite 



Melilite-Basalt 













Alkalic or 

 Lime-soda — 



(Mafic) 



Theralite 



Shonkinite 







Monchiquite ? 



(glass-base.) 



Basanite 



( + 01iv.) 



Feldspars -f 

 Nephelite. 







Tephrite 



(-Oliv.) 



Lime-soda 



Feldspars + 



Alkalic minerals 



(Mafic) 



Essexite 



Essexite- 

 porphyry 



Gaute'lte 



Camptonite 



Trachydolerite 



Lime-soda 

 Feldspars 

 (Andesine) 



Diorite and 

 Quartz- 

 Diorite 



Diorite- 

 porphyrite 



Malchite 



Kersantite 

 Spessartite 



Porphyrite 



(+ or —quartz) 

 Dacite (Vqtz.) 

 Andesite(— qtz) 



Lime- soda 



Feldspar 



(Labradorite) . 



4- Pyroxenes. 



Gabbro and 

 Norite 



Gabbro 

 porphyrite 



Beerbachite 



Odinite 



Diabase 

 Basalt 



No feldspar 



only 

 Mafic mins. 



Peridotite 

 Pyroxenite 









Picrite- 

 porphyrite 















