398 



the crystallization of minerals in igneous rocks. Seeing that the order of 

 separation of minerals in igneous magmas depends not only upon the 

 characters of minerals (e.g., fusibility and composition), but also on the 

 composition of the magma it is impossible to draw up a table which will 

 express the order of consolidation in all cases. The following is the 

 general order according to LAGORIO: Oxides, Fe-silicates, Mg-silicates, 

 Fe + Mg-, Mg + Ca-, Mg + K- (or Fe + K-), Ca-, Ca + Na-, Na-, 

 and lastly K-silicates. Free SiO 2 may crystallize out before, after or 

 simultaneously with K-silicates. 



The general subject of the crystallization of minerals in igneous 

 magmas has been discussed in Chapters II. and III. The conclusions there 

 laid down have been confirmed and extended by LAGORIO in the important 

 paper already referred to, which has appeared since those chapters were 

 written. We will now quote some additional facts which have been 

 established by LAGORIO. First as regards the acid rock's. 



Si0 2 



A1A 



Fe 2 3 



CaO 



MgO 



K 2 



Na 2 



Loss 



Sp. Gr. 



Si0 2 



A1 2 3 



Fe 2 3 



CaO 



MgO 



K 2 



Na 2 



Loss 



Sp. Gr. 



99-12 99-98 99-85 ... 100-30 ... 99'79 



2-1328 



2-1121 



2-2105 



2-0891 



2-5232 



100-58 



2-359 



100-54 



2-4080 



99-01 



2-8235 



99-96 



2-4005 



100-20 



2-647 



I. Glassy base of a spherulitic obsidian from Lipari. The order of consolidation of 

 constituents in this rock was, 1st, belonites and magnetite, 2nd, spherulites. 



II. Spherulite from the same rock. The spherulites give a black cross. 



III. Glassy base of a spherulitic obsidian from Teneriffe. Order of consolidation of con- 

 stituents, 1st, microlites and trichites, 2nd, spherulites. 



IV. External portion of spherulite from the same rock. 

 V. Internal portion of spherulite from the same rock. 



