The Binary System Akermanite-Gehlenite. 139 



values of the specific volumes for glasses and crystals of 

 the composition of akermanite, gehlenite, and several 

 intermediate mixtures. In fig. 4 curves for the specific 

 volumes plotted against the composition in weight per- 

 cent are shown. 



Table IV 



Specific volumes of artificial crystals and glasses of the Aker- 

 manite-Gehlenite series. 



Composition 



wt. percent Sp. vol. Sp. vol. 



Akermanite. Gehlenite. crystals. 





 25 

 50 



75 

 100 



100 



75 

 50 



25 

 



90.4 



90.8 

 91.5 

 92.1 



92.8 



95.2 

 94.5 

 93.8 

 93.1 

 92.4 



O /O 10 

 GEHLEM/T£ 



30 40 SO 60 

 WT. P£RC£/YT 



?0 80 o JO /oo 



Fig. 4. — Specific volumes plotted against composition in weight percent, 

 for crystals and glasses. 



Vogt 12 has discussed the relations of akermanite and 

 gehlenite as interpreted from a study of slags. He con- 

 cludes that they mix to form an isomorphous series, 

 and finds that the birefringence of certain inter- 

 mediate mixtures decreases to zero at a certain intermedi- 

 ate composition. The formulae assumed by Vogt for geh- 

 lenite and akermanite, however, differ from those used by 

 us, and many of the materials studied by Vogt contain 

 iron, manganese, soda, and other impurities, so that the 

 data he obtained are from more complex mixtures than 

 the system discussed by us. 



A further investigation of the minerals of the melilite 

 group is contemplated, and a more thorough discussion 

 awaits its completion. 



12 J. H. L. Vogt, Mineralbildung in Schmelzmassen, 96-176. 



