ART. 2 PEOPERTIES OF GLAUCONITE — ROSS 9 



The foregoing considerations indicate that the chemical composi- 

 tion of glauconite can be completely explained if it is considered to 

 be an isomorphous mixture of two end members with the formulas 



(A) = 2H2O ■ K2O ■ 2 (MgO, Fe'^ O) • 2 (Fez^^^Og, AI2O3) • lOSiOz + 3H2O 

 and 



(B) =2H20.K20- (MgO,Fe^^O) -SCFea'^^Oa.AlaOa) -lOSi O2 + 3H2O 



The two formulas are nearly identical, the only difference being 

 that in (A) there is 2MgO instead of IMgO as in (B), and this 

 is compensated for by there being 1 FegOs less in (A) than in (B). 

 These formulas may be written in several different forms as follows : 



(A)=4H-2K-2Mg-4Fe^^^-10Si -SlO + SHzO 

 and 



(B)=4H-2K-Mg-6Fe^^^-10Si-33O-l-3H2O 



There is an excess of but one oxygen over the 1 to 3 ratio of the 

 silicic acid, and in order to make this compound a metasilicate this 

 oxygen can theoretically be combined only with the ferric iron so 

 that the formulas may be written : 



A=4H-2K-2Mg.[Fe^^^O]^.3Fe^^'-10[SiO3]+3H2O 

 and 



B=4H-2K-Mg-3[Fe^^'OK-3Fe^^^-10[SiO3] + 3H2O 



