SOIL MINERALS IQ\ 



These silicic acids are either unknown or but little known 

 in the free condition but their salts are very common among 

 the silicates which constitute most of the soil minerals. 



The most important potassium silicate is a double tri- 

 silicate of potassium and aluminium called orthoclase or the 

 potash feldspar. Its formula is KsAIsCSisC^s. It is frequently 

 written K 2 O.Al 2 03.6Si02 which shows its composition but 

 not its chemical structure. Written graphically it is: 



Al 



It occurs in monoclinic crystals of flesh-red, yellow, or white 

 color. In pure water orthoclase is but very slighly soluble, 



