224 C. N. Fenner— Crystallization of a Basaltic Magma 



dimensions are "15 by *03 mm , but occasionally crystals of larger 

 size up to l mm in length, and more nearly equidimensional, 

 are scattered through the mass. It comprises, roughly speak- 

 ing, two-fifths of the whole. 



Fig. 5. 



Fig. 5. Photograph of normally crystallized basalt. (Slide No. 18.) 

 Diameter of field 2i mm . 



Fig. 6. 



Fig. 6. Opliitic texture of normally crystallized basalt. (Slide No. 47.) 

 Plagioclase laths, diopside grannies, and crystals and dust of magnetite in 

 mutual intergrowth. The magnetite is mostly included in the diopside, 

 but partly also in the plagioclase. Diameter of field r5 mm . 



Extinction angles measured on symmetrically extinguishing 

 albite twins give maxima of 33-34 degrees. This indicates 

 a medium labradorite of about the composition Ab 40 An 60. 



The pyroxene is in stouter forms of an irregularly angular 

 outline. The grains show a tendency to coalesce in groups of 



