PETROLOGY OF SOME LIMESTONES FROM THE ANTARCTIC 



197 



took several grammes of the rock, ground it very fine, and took one gramme from this 

 powder for a bulk analysis. The result is as follows: 



SiO„ 



A1 2 3 



Fe o 3 



Feb 



Ti0 o 



CaO" 



MgO 



K 9 



Na 2 



co; 



H 2 - (below 110°) 

 H 2 + . . . 



= 22-19 



= 6-05 



= 1-30 



= 1-55 



= 0-55 



= 34-44 



: 1-98 

 : 2 51 

 : 1-96 



= 26-55 

 •46 

 •92 



100-46 



An attempt was made to determine the composition of the green material by 

 dissolving the carbonates in dilute hydrochloric acid (1 in 6) and analysing the 

 insoluble residue. It was found, however, that the acid had attacked a part of the 

 green material, since 2 per cent, of Si0 2 and 3 per cent, of A1 2 3 occurred in the 

 soluble portion, and this attempt was abandoned. The composition of the green 

 material was eventually arrived at by alloting all the C0 2 to the lime and magnesia 

 in the analysis and expressing the result as carbonates of lime and magnesia. For 

 this purpose the assumption was made that the carbonates are present in the rock in 

 the same proportions as the oxides in the analysis. In this way the carbonates were 

 determined as follows: 



CaC0 3 . 

 MgCO, . 



56-82 

 2-98 



59-80 



After satisfying the carbon dioxide with lime and magnesia an excess of 2*62 per 

 cent, of the former and -56 of the latter remained, which was allotted to the remainder 

 of the rock. This has the composition shown in Column I. Calculated to 100 per cent, 

 it is shown in Column II. 



Si0 o 



A1 2 3 



Fe,0 3 



FeO 



TiO„ 



CaO 



MgO 



K o 



Na. 7 



H 6 - 



H 2 + 



40-67 



99-96 



11 



2E 



