SOME CONCEPTIONS OF THE SOIL 



of soil almost always come directly from tlie original rock 

 as do particles of orthoclase, biotite, and apatite. Hematite, 

 the kaolinite group and the chlorite and epidote groups 

 generally originate in soils through weathering. The fol- 

 lowing list of minerals is by no means complete, yet it includes 

 the more important forms from the soil and plant standpoint. 



A LIST OF THE MOST IMPORTANT SOIL MINERALS.* 

 (The elements in bold type are those necessary for plant nutrition.) 



1. Quartz 



2. Orthoclase and 

 Mierocline feldspar 



3. Muscovite mica 



4. Biotite mica 



5. Plagioclase feldspar 



6. Calcite and Dolomite 



7. Hornblende and Augite 



8. Olivine 



9. Apatite 



10. Kaolinite group 



11. Serpentine and Talc 



12. Chlorite group 



13. Epidote group 



14. Hematite 



15. Limonite group 



SiOs 



KH2Al3Si30i3 

 KHMgFeAl^SiaOia 

 Ca and Na aluminum silicates 

 CaCOs and (Ca, Mg) CO3 

 Ca, Mg, Fe aluminum silicates 

 (Mg, Fe)2Si04 

 Oa, (P0J3(C1,F) 

 Typified by kaolinite. 



JUL /I xxxo 10 -Lo ^-^ 9 



Hydrated Mg silicates 

 Hydrated Mg, Fe aluminum 



silicates 

 Hydrated Ca, Fe aluminum 



silicates 



St '^o^-' 3 



Typified by limonite 2 PeaOg. 

 3 H2O 



^ Below are some of the most important mineralogical investigations of 

 soil: MeCaughey, W. G-., and Williams, H. F., The Microscopic De- 

 termination of BQil-Forminff Minerals; U. S. Dept. Agr., Bur. Soils^ BuL 

 91. 1913. Plummer, J. K., Petrography of Some North Carolina 

 Soils and Its BelationsUp to their Fertiliser Bequ-irements, Jour. Agr. 

 Ees., Vol. V, No. 13, pp. 569-581. 1915. Eobinson, W. 0., The Inor- 

 ganio Composition of Some Important American Soils; XT. S. Dept. Agr., 

 Bui. 122, Aug., 1914. 



