42 ALBERT JOHANNSEN 



represent the various ores; the writer, however, groups the ores 

 in one family, for, considered as rocks, they are unimportant and 

 hardly worth separating. 



THE MINERAL GROUPS 



The constituents of the rock are divided into three primary 

 groups : 



QUARFELOIDS 



(Qu) Quartz 



(Kf) Orthoclase, microcline, microperthite, anorthoclase, etc. 

 (Plag) The whole isomorphous Ab-An series of plagioclases 

 (Folds) The feldspathoids (nephelite, leucite, sodalite, hauynite, noselite, 

 melilite, primary analcite, etc.) 



MAriTES 



Dark micas (biotite, phlogopite, etc.) 



Amphiboles 



Pyroxenes (including uralitized pyroxene) 



Olivine 



Iron "ores" (magnetite, ilmenite, chromite, pyrite, hematite, etc.) 



Cassiterite 



Garnet 

 Minor I Primary epidote 



Mafites 1 Allanite, zircon, rutile, primary titanite, spinel, and other dark 

 minor constituents 



AUXILIARY CONSTITUENTS 



The auxihary constituents are seldom of importance. 



Topaz Primary scapolite 



Tourmaline Primary calcite 



Cordierite Muscovite 



Corundum LepidoUte 



Fluorite Zinnwaldite 



Andalusite Apatite, etc. 



Most of the auxiliary constituents are light in color; they are, 

 consequently, computed among the leucocrates. 



SECONDARY CONSTITUENTS 



Secondary constituents are to be calculated as the originals from 

 which they came. Thus ore replacements of the mafites are com- 

 puted as mafites, kaolin as feldspar, etc., chlorite as a biopyribole, 

 analcite as feldspathoid, pseudoleucite as leucite, etc. 



