ARGILLITES AND SHALES 



119 



Chemical Composition op Kaolins an3> Other Clays 



CONSTITITENTS 



Si02 (combined) 

 Si02 (free) , , 

 AlaUg ■ - . I 

 H2O (combined) 

 H20at212'=» . , 

 CaO and MgO 

 Alkalies. . . , 

 FcaOs . . , , 



46.4 % 

 . * • • 

 39.7 

 13.9 



99.00 % 



II 



39.00% 



36.00 

 14.00 



9.50 



0.63 



0.54 



99.67% 



III 



34.70% 

 12.20 

 31.34 

 12.00 



8.00 



0.10 



0.95 



0.16 



99 45% 



IV 



28.30 % 



27,80 



27.42 



6.60 



2.90 



0.18 



2.71 



2.68 



98.59% 



42.71 % 

 0.70 

 39.24 



lo.OiU 



1.68 

 0.20 

 0.89 

 0.46 



99.10% 



YI 



}60.97% 

 26.38 

 } 8.93 



} 1.90 

 1.46 



99.64% 



I. Kaolin. II, Indianite, a white clay residual from St. Lawrence County, 

 Indiana III, Potter's clay, from Pope County, Illinois. IV. Brick clay 

 from New Jersey. V Pire clay from New Jersey. VI Fire clay from 

 Illinois. 



Amongst the older formations tlie clays have largely under- 

 gone induration, giving rise to what are known as argillites, or 

 if fissile, slates or clay slates^ such as are nsed for roofing and 

 similar purposes, the fissile property having been imparted by 

 pressure or shearing. Such forms pass by imperceptible grada- 

 tions into argillaceous schists which are classed with the meta- 

 morphie rocks. (See p, 135.) The argillites are, as a rule, 

 among the most indestructible of rocks, since they are them- 

 ■selves composed of the least destructible debris of pre-existing 



Chemical Composition of Aegillites. 



Constituents 



I 



II 



III 



Silica (Si02) ....... 



Sulphuric acid (H2SO4) 



Alumina (AlgOs) 



Iron oxides (FeO) and (EegOs) . . 



Lime (CaO) 



Magnesia (MgO) 



Soda (Na20) . . , 



Potash (K2O) , 



Water (H2O) 



58 37% 

 0.22 

 21.985 

 10.661 

 30 

 1.203 

 1.933 



4.03 



60.32% 



23.10 

 7.05 



0.87 

 49 

 3.83 

 4.08 



60.150% 



24.20 

 7.65 



• • % . 



- 4.278 

 3.72 





98.702% 



99.74% 



99.998% 



