226 C. 1ST. Fennev — Crystallization of a Basaltic Magma 



liquid, the plagioclase is bounded by plane faces, while the 

 diopside has irregular outlines, and it appears that this differ- 

 ence in development is due to the mode of growth, the cause 

 of which is not germane to the subject. When, in the more 

 glassy types, the plagioclase and diopside form groups of 

 intergrown crystals, as they often do, the characteristic form 

 is shown in tig. 7, a notable feature of which is the manner 

 in which the plagioclase laths wedge out toward the central 

 portion of the diopside grains. 



Fig. 7. 



Fig. 7. Intergrowtli of diopside and plagioclase. (Slides Nos. 2 and 57.) 



These features are apparent in all phases of development of 

 the basalt from glassy to noncrystalline, and alone would be 



Fig. 



O'S* m />■?. 



Fig. 8. Modification of forms of plagioclase and diopside resulting from 

 simultaneous crystallization. A few magnetite grains (black) and some 

 chlorite (gray) are also present (Slide No. 64). 



almost conclusive evidence of simultaneous growth of the two 

 minerals. 



