162 JV. L. JBowen — Crystallization of Haplobasaltic, 



NH 4 C1 solution, MgO obtained by igniting the precipitated 

 carbonate to constant weight, specially prepared CaC0 3 and 

 silica as ground quartz purified by heating with HC1. 



Optical Properties of the Crystalline Phases. 



The crystals obtained throughout the work were in nearly 

 all cases very small and no precise measurements of optical 

 properties were undertaken. It was necessary only to deter- 

 mine such properties as permitted the distinguishing of diop- 

 side from plagioclase. 



The diopside occurred usually in stout crystals with pris- 

 matic elongation and strong birefringence. The plagioclases 

 had a pronounced tabular development j| 010, the plates being 

 often so thin that when viewed in plan (rhomb sections) their 

 birefringence was barely discernible, whereas viewed on edge 

 (needle sections) the birefringence was marked. 



The refractive indices of the plagioclases were usually not 

 very different from those of the glasses in which they were 

 embedded, whereas the diopside indices were always con- 

 spicuously higher. In the mixtures rich in albite the crystals 

 were always very minute and the indices of the plagioclase 

 crystals were considerably higher than the glasses. The plagio- 

 clase crystals of these mixtures were, however, readily dis- 

 tinguished from diopside by their low extinction angles and 

 negative elongation, whereas diopside has extinction angles up 

 to 38° and those sections with low extinction have positive 

 elongation. 







Table I. 





Composition 



Tempera- 







iopside 



Anorthite 



ture 



Time 



Result 



80 



20 



1348 



£hr. 



Glass and diopside 



80 



20 



1352 



inr. 



Glass only 



60 



40 



1275 



£hr. 



Glass and diopside 



60 



40 



1280 



i hr. 



Glass only 



60 



40 



1272 



£hr. 



Glass and diopside 



60 



40 



1268 



ihr. 



Diopside and anorthite 



50 



50 



1326 



ihr. 



Anorthite and glass 



50 



50 



1330 



4hr. 



Glass only 



50 



50 



1268 



|hr. 



Diopside and anorthite 



50 



50 



1272 



£hr. 



Glass and anorthite 



40 



60 



1388 



Ihr. 



Glass and anorthite 



40 



60 



1392 



ihr. 



Glass only 



20 



80 



1483 



*hr. 



Glass and anorthite 



20 



80 



1487 



£hr. 



Glass only 



