586 CROSS, ID DINGS, PIRSSON, WASHINGTON 



The femic minerals are here dominant and those of the salic 



group subordinate. 



_ 7 rT sal i . : 



C/ass V: - — < - , per rem ic. 



rem 7 



The rocks of this Class are extremely rich in the femic min- 

 erals — pyroxenes, olivine, magnetite, etc. 



Subclasses. — The next step in the systematic subdivision 

 takes account of the distinctions among the standard minerals 

 constituting the salic and femic groups. There being a consid- 

 erable number of these minerals in each group, it is necessary for 

 reasons already given to divide each group into two parts. Of 

 the salic minerals, quartz, feldspar and the feldspathoids form a 

 closely associated series when considered petrographically and 

 chemically, and may be contrasted with corundum, zircon or 

 other salic minerals. Group I, therefore, falls into Part I, 

 quartz, feldspars and feldspathoids, indicated in certain abbrevi- 

 ated expressions by the letters Q, F and L, and into Part 2, 

 corundum, zircon, etc., indicated respectively by C and Z. 



Part 1. Quartz (Q), Feldspars (orthoclase, albite and 

 anorthite) (F). Feldspathoids (leucite, 

 Group I. \ nephelite, sodalite, noselite) (L). 



[ Part 2. Corundum (C) and Zircon (Z). 



Similarly, of the femic minerals, the pyroxenes, olivine, 

 akermanite, magnetite, ilmenite and titanite are closely associ- 

 ated in rocks, and form frequent transitional series of rocks with 

 different proportions of these minerals. They may be grouped 

 together as Part I of Group II, and contrasted with apatite, 

 fluorite, pyrite, the metals and other femic minerals constituting 

 Part 2. In abbreviated expressions minerals of Part I are indi- 

 cated by the letters P, O and M, those of Part 2 collectively by A. 



Part 1. Pyroxenes (diopside, hypersthene, wollas- 

 tonite and acmite) (P). Olivine and aker- 

 Group II. X manite (O). Magnetite, hematite, ilmenite, 



r utile, per of skite and titanite (Mi). 

 Part 2. Apatite, fluorite, pyrite, etc. (A). 



