206 



EOCK BISINTEGBATION AND DECOMPOSITION 



an almost complete loss of alkalies. In the second stage (column 

 III) lime and magnesia are both lost in considerable amounts^, 

 the iron passing over wholly to the condition of sesquioxide, and 

 there is a further slight diminution in the proportional amount 

 of silica. It is evident that here the feldspars were the first of 

 the constituents to yield to the decomposing forces, the augite 

 and olivine proving most refractory. The total loss of material, 

 it will be noted, amounts to 43.96%, the lime, magnesia, alka- 

 lies, iron oxides, and silica disappearing in the order here 

 mentioned. 



In the case of the basalt from Crouzet, the analyses show a 

 total loss of 60.12%, or over one-half of the original material. 

 This loss includes nearly two-thirds of the original silica, 



Analyses of Fresh and Decomposed Basalt from the Haute Loire, 



France 





I 



n 



in 



IV 



Y 



CONSTrrUBNTS 



w 

 



1 



CQ 



S § fl 



OSS 



*? S c. 







 a 



□Q 



til 



M 



3I 



w 



iS i ^ 



S E^ 



■*' » s 



b K ^ 



|53 



W E^ 











M 63 9 



M 9 K 



« "3 a 





w 



w 



Wo"? 



« ^ s 



M << U 





pq 



p« 



f^H g« 



P-.W B 



^ W B 



Silica (SiOj) .... 



48.29 % 



37.09% 



30.34% loss 



34.44 % 



66.56 % 



Alumina (AI2O3) . . . 



13.25 



30.75 



0.00 *' 



100.00 



0.00 



Ferric iron (FegOg) . . 

 Ferrous iron (FeO) . . 



0.00 

 16.66 



4.3n 



0.00 J 



16.64 *« 



1L16 



88.84 



Lime (CaO) .... 



7.33 



8.97 



3.46 " 



52.76 



47.24 



Magnesia (MgO) . . . 



7.03 



0.61 



6.77 *' 



3.62 



96.38 



Potash (K2O) .... 



1.81 



0.71 



1.51 " 



16.66. 



83.34 



Soda (Na20) .... 



2.71 



1.01 



1.40 " 



25.59 



74.41 



Ignition 



4.92 



16.55 



0.00 



100.00 



0.00 





100.00 % 



100.00% 



60.12% 



« « w « 



• • * • 



88.84% of the iron, and 96.38% of the magnesia. The loss 

 of both iron and magnesia in such proportionally large quan- 

 tities is quite unusual, and indicates, so far as the iron is con- 

 cerned, that the decomposition took place under conditions 

 excluding a sufficient supply of oxygen to convert the same 

 into the insoluble sesquioxide, or where subjected to the de- 



