Buddington — Natural and Synthetic Melilites. 59 



field of solid solution lying along the line between 2CaO. 

 Mg0.2Si0 2 and 3CaO.Al 2 3 .3Si0 2 and restricted to the 

 3CaO.Al 2 3 .3Si0 2 end. However, if the compositions are 

 plotted upon a triangular diagram, there is a zone extend- 

 ing from the component 3CaO.Al 2 3 .3Si0 2 to about the 

 center of the line connecting the components 2CaO.MgO. 

 2Si0 2 and 3CaO.Fe 2 3 .3Si0 2 in which the preparations 

 lack but a trifle of being completely homogeneous. Tables 

 IX-XII give the optical and thermal data for the mixtures 

 investigated. 



Fig. 9. 



1-690 



c; /-680 



X 1-670 

 v 1-660 



tj 1-650 



X 



1-630 







1 



3 

























CO 



< 



l 







/.-} 



\*r 









,-< 













\ 











20 



40 CO 



90[£Ca0-Mg0-23L0 a ] WT-PERCENT 



ZO[J Na 2 0-^/ e Oj- J^i O z l 



1-700 

 1-690 

 l-6d0 

 1-670 

 1-660 

 I-65Q 



90C3CaO-r e ^ OyJJl OJ 

 lO[JA/c^^D-/\l a 3 -35L O z ] 



9. — Curves for refractive indices plotted against composition in weight 

 percent for mixtures crystallized just below the solidus which show complete 

 homogeneity. Indices of refraction for dominant phase of inhomogeneous 

 mixtures are indicated when determined. 



Fig. 9 shows the refractive indices plotted against the 

 composition in weight percent for those compositions 

 that lie along the line connecting the components 2CaO. 

 Mg0.2Si0 2 and 3CaO.Fe 2 3 .3Si0 2 , the amount of 3Na 2 0. 

 Al 2 3 .3Si0 2 being kept constant at 10 percent. The 

 curves connect only those compositions which were found 

 to form completely homogeneous mixtures within a tem- 

 perature range lying above 1000°, the lowest temperature 

 at which observations of these mixtures were made. In 

 the case of those mixtures which showed inhomogeneity, 

 the indices of refraction for the dominant phase are 



