172 THE SOIL: INORGANIC MATTER 



noted above to kaolinite, which is an aluminium mineral. 

 In addition there are bauxite, Al 2 0(OH) 4 , 



OH 



/ 



Al— OH 



\ 



O 



/ 

 Al— OH 



\ 

 OH 



rounded grains or clay-like masses, white or yellowish in 

 color; and wavellitc, Al 3 (OH) 3 (P04)2, 



radiating crystals occurring in hemispherical masses. 



136. Factors of Solubility. — From the above discussion of 

 the solubilities and decomposition products of soil minerals 

 it might be thought that solution was easy and the reactions 

 fairly simple. But it must be emphasized that under actual 

 conditions the reactions only approximate those indicated. 

 That is, only a part of any mineral actually decomposes as 

 far as stated. Reactions are not complete, and while in 

 the case of a feldspar, for example, some potassium car- 

 bonate and kaolinite are formed, and formed continually 

 although slowly, much of the mineral remains unaltered and 

 some of it decomposes only partly. Intermediate compounds 

 are formed. Other compounds interfere and react with the 

 original mineral or with its decomposition products. Much 

 more so is this true of more complex minerals. 



Temperature has a decided effect on these reactions in the 

 soil. The higher the temperature the more active the 



