Buddington — Natural and Synthetic Melilites. 13 



dissociation. Below the solidus for mixtures of these 

 two components, however, solid solution does exist for 

 limited ranges of temperature and of composition. 



Table III. 



Optical and thermal data for mixtures of 2CaO.AL0 3 .Si0 2 and 3CaO.Al 2 3 . 



3Si0 2 . Compositions expressed in weight percent and 



temperature in degrees Centigrade. 



2CaO. 



3CaO. 







One 



Trace of 



Glass 





AL0 3 



ALO3. 















Si0 2 



3SiO., 



nco 



ne 



phase 



ciation 



crystals 



All glass 



100 







1.669 



1.65S 









1590° 



75 



25 



1.658 



1.650 



1145° 

 (1 hr.) 



*1170° 

 (1 hr.) 



1566° 



1574° 



50 



50 



1.648 



1.642 



1110° 

 (1 hr.) 



1150° 

 (1 hr.) 



1524° 



1530° 



35 



65 



tl.643 



tl.635 



Trace dissoc. 



1484° 



1490° 











(16 hrs. 



at 980°) 







20 



80 



tl.642 



tl.633 



Inhomogeneous 



1428° 



1433° 











(16 hrs. 



at 980°) 











100 







Inhomogeneous 



1340° 



1347° 











(16 hrs. 



at 980°) 







*The dots thought to represent dissociated products are so small in 

 amount, and so minute, that this determination is doubtful, and this 

 mixture may be homogeneous up to the eutectic. 



t Determined on major crystal phase. 



In Table III are given the optical characters and 

 thermal data for the mixtures of these two compounds 

 which were investigated. Owing to the very finely fibrous 

 character of the preparations crystallized some distance 

 below the eutectic, it is very difficult in many cases to 

 determine the homogeneity or inhomogeneity of the 

 material under examination. For this reason no impor- 

 tance is attached to the temperatures given as marking 

 the beginning of dissociation, and the limits of solid solu- 

 tion are likewise only approximations. The end compo- 

 nent, 3CaO.Al 2 3 3Si0 2 when held for 16 hours at 980° 

 gave a fibrous aggregate which was conspicuously inho- 

 mogeneous. Filaments of a mineral, presumed to be 

 wollastonite, are prominent. A mixture containing 20 

 percent of 2CaO.Al 2 3 .Si0 2 , heated for 16 hours at 980°, 

 likewise gave a conspicuously inhomogeneous fibrous 

 aggregate, but not to such an extent as the end member 

 alone. With an increasing percentage of 2CaO.Al 2 3 . 

 Si0 2 the evidence of inhomogeneity decreases and in a 

 mixture of the composition 35 percent 2CaO.Al 2 3 .Si0 2 -65 



