PETROGRAPHIC TERMS FOR FIELD USE 321 



neous rock, consisting almost entirely of one or more members 

 of the pyribole group. It includes the pyroxeneids and amphibo- 

 leids, and corresponds to dolereid among the feldspar rocks. 



Peridoteid. — A noncrystalline, medium- to coarse-grained ig- 

 neous rock, consisting of olivine, with or without pyriboles. Feld- 

 spar is absent. This group includes the peridotites. 



II. APHANEIDS 



Felseid. — An aphanitic igneous rock, non-porphyritic and light- 

 colored. Here are included non-porphyritic rhyolites, trachytes, 

 phonolites, latites, and the light-colored andesites. They are leuco- 

 aphaneids (A-ey/co?, "white"). 



Felseid porphyry. — Under this head are grouped all light-colored 

 porphyritic igneous rocks with aphanitic ground-masses. They 

 may also be called leuco phyreids . 



Quartz felseid porphyries or quartz leucophyreids are those 

 felseid porphyries among whose phenocrysts quartz can be recog- 

 nized. Other mineral modifiers, such as orthoclase, biotite, horn- 

 blende, etc., may be used for different varieties. 



Anameseid. — An aphanitic igneous rock, non-porphyritic and 

 dark colored, generally dark gray, dark green, dark brown, or 

 black. In this group are included the dark andesites and basalts. 

 They are melano-aphaneids (^ekavos^ "dark"). 



No sharp line can be drawn between these rocks and the fel- 

 seids. The relative amounts of the dark and the light con- 

 stituents cannot be determined megascopically, and it is only 

 possible to classify the felseids by their colors, which are white, 

 yellow, light brown, pink, and pale gray. 



Basalt, being such an overworked word, von Leonhard's term 

 anamesite was chosen instead as the root. It was originally applied 

 to basaltic rocks of such fine texture that the constituents were 

 indistinguishable megascopically. 



Anameseid porphyry. — In this group belong all dark-colored 

 porphyritic igneous rocks with aphanitic ground-masses. The 

 term melanophyreid may also be used. If the phenocrysts can be 

 determined, their names may be prefixed, as biotite melanophyreid 

 or biotite anameseid porphyry, etc. 



