CHEMICAL COMPOSITION OF ABSAROKITE. 



329 



The chemical composition of six of these rocks is shown by the follow- 

 ing analyses, the characteristic features of which have already been 



indicated : 



Analyses of dbsarokites. 



Constituent. 



1 



2 



3 



i 



5 



6 



SiO» 



48.28 



.88 



11.56 



3.52 



5.71 



.13 



48.95 



.49 



12.98 



3.63 



4.68 



.13 



48.36 



1.18 



12.42 



5.25 



2.48 



.13 



.29 



9.36 



8.65 



1.46 



3.97 



.84 



Trace. 



51.76 



.47 

 12.36 



4.88 



4.60 



.11 



49.71 



1.57 



13.30 



4.41 



3.37 



.17 



.46 



7.96 



8.03 



1.49 



4.81 



.66 



Trace. 



51.68 

 1.08 



14.07 



4.71 



4.57 



Trace. 



TiO, 



FeO 



MnO 



BaO 



MaO 



13.17 



9.20 



2. 73-2. 89 



2. 17-2. 22 



.59 



11.73 



7.66 



2.31 



3.96 



.67 



9.57 

 7.14 

 1.99 

 3.83 

 .56 



7.72 



6.65 



2.45 



4.16 



.72 



S0 3 . 13 



Li»G Trace. 



2.09 



CaO 



Cr O 



CI 



.18 

 2.96 







Total 



Less for CI 



3.16 



5.54 



3.05 



4.07 



100. 08 

 .04 



100. 35 



99.93 



100. 32 



100. 01 



100. 03 



100. 04 



1. Leucite-absarokite, Ishawooa Canyon, Wyoming. Analyst, J. E. Whitfield. (1698.) 



2. Absarokite, dike at head of Lamar River. Analyst, L. G. Eakins. (1306.) 



3. Absarokite, dike south of Clark Fork River. Analyst, L. G. Eakins. (1277.) 



4. Absarokite, lava flow, head of Raven Creek. Analyst, L. G. Eakins. (1151.) 



5. Absarokite, dike, divide east of Cache Creek. Analyst, L. G. Eakins. (1282.) 



6. Absarokite, lava flow, Two Ocean Pass. Analyst, J. E. Whitfield. (1720.) 



The six analyses are arranged according to decreasing percentage of 

 magnesia. The first two have the highest; the second two, over 9 per cent; 

 the fifth and sixth have 7.96 and 7.72, which are not very high for a rock 

 so -low in silica. There is an increasing range in alumina and in potash. 

 The second, third, and fourth analyses are closely alike. The first and last 

 two are not so much alike that they might not be considered separately. 

 The chief differences are in the magnesia and alkalies, but they are related 

 in other respects. They all exhibit considerable loss upon ignition, corre- 

 sponding to the amount of hydration due to alteration or to the presence of 

 zeolitic minerals. 



As alreadv said, the rocks here grouped together differ somewhat in 



