399 



VI. Glass of spherulitic obsidian from Cerro del Quinche, Quito. ProbalVe order of con- 

 solidation in the rock, 1st, opaque grains and belonites, 2nd, felspar, 3rd, quartz, 4th, 

 spherulites. 



VII. Spherulite from the same rock. 



VIII. Glass of a spherulitic rock from Ecuador. Order of consolidation of constituents 

 in the rock 1st, trichites, Lelonites and magnetite, 2nd, striated felspar (anorthoclase), 3rd, 

 spherulites. 



IX. Spherulite from the ame rock. Shows a feeble cross in polarized light. 

 X. Felspar (anorthoclase) out of same rock. Extinction on P + 330' on M + 7'lo'. 



A consideration of these and other analyses given by LAGORIO 

 points to the conclusion that in a magma rich in silica and the 

 alkalies and poor in lime and magnesia, the Na0-silicates tend to 

 separate out in preference to the K^O-silicates. Thus the spherulites 

 are richer in soda than the glass. Moreover, the felspar in the rock 

 from Ecuador is richer in soda than the Spherulite in the same rock ; 

 it is essentially a soda-felspar. It follows also from LAGORIO'S analyses 

 that the spherulites contain a slightly higher silica-percentage. This, 

 however, may be simply a consequence of the former fact for Na^O- 

 silicates contain more silica than the corresponding K 2 0-silicates, 

 because the atomic weight of Na is lower than that of K. K 2 0- 

 silicates can separate out only when they are present in great quantity. 

 According to LAGORIO, the molecular ratio of K 2 O : Na 2 must be at 

 least as high as 2:1 before sanidine can form, and even then it 

 contains a considerable amount of Na 2 O. 



As regards the intermediate rocks, LAGORIO'S researches merely 

 confirm the results already given in Chapter II, as may be seen from 

 the following analyses. 



Si0 2 



A1A 



FeA 



Cab 



MgO 



K 



Na 2 



Loss 



100-17 



99-31 



Sp. Gr. 2-7651 2-6186 



100-70 

 2-6850 



99-42 



99-47 



2-5410 2-2540 



99-40 

 2-5673 



