takr] 



COMMOX ROCKS 



CLAs:^H-lCA110.\ Ol- ll.-\KoL> ROCKS, (alter I'irrson > 



I Grained, constituent grains recognizable. Mostly intrusive. 



I'erromagnefian rocks, general- 

 ly dark to black 



Ncn- 

 |>orphyritic 



Porphyritic 



With rubordi- 

 nate feldspar 



Dolerite 



Dolerite- 

 porphyry 



Without 

 feldspar 



Peridotite 

 (rare) 



II Dense, constituents wholly or partly unrecognizable. Mostly extrusive rocks. 



Xor- 

 porphytitic 



Porphyritic 



Li.a:;it-colored, white, light gray, 



red, \^eriow, brown, light and 



medium green. Usuallj' isld- 



r.pathic 



Felsite 



Felsite-porphyry 



Dark-col ared to black, very dark 

 green or very dark gray. Usual- 

 ly ferromagnesian 



Basalt 



Basal t-por])hyry 



III Rocks composed wholly or partly of glass. Extrusive. 



Obsidian, pitchr.tone, pumice, rarely porphyries of thess. 



I •>" i'racrmertal volcanic material. tuiY, volcanic a5"li. 



Figure 4. — Granite from the Booth Cjuarry, Waterford. Show- 

 ing granitic texture. 



