52 Buddington — Natural and Synthetic Melilites. 



Temperature Time Phases 



1260° 24 hrs. Euhedral tetragonal crystal plus glass. Crystal 



habit is thick tabular, pseudo-cubic, and short 

 prismatic; combination of 1st order prism 

 and base alone, or 1st and 2d order prism and 



no, = 1.651 ne— 1.636 



1320° 72 hrs. Glass plus euhedral crystals, similar to pre- 



ceding. 



no, — 1.656 ne = 1.645 



1327° 1 hr. Glass plus trace of crystals. 



1334° 1 hr. AU glass. 



Table VII. 



Optical and thermal data for mixtures of 2CaO.Al 2 3 .Si0 2 and [(90 



3CaO.Al 2 3 .3Si0 2 ) (10 3Na,O.Al 2 3 .3Si0 2 ) ] Compositions expressed 



in weight percent, and temperatures in degrees Centigrade. 



90 2CaO.Al 2 3 .Si0 2 — 10 [ (90 3CaO.Al 2 3 .3Si0 2 ) (10 3Na 2 O.Al 2 3 .3Si0 2 ) ] 



Phases 



Fibrous granular aggregate with sutured tex- 

 ture. Clear and homogeneous single crystal 

 phase. 



Coarse crystalline aggregate with faintest trace 

 of glass. Ww = 1.664 ne = 1.654 



Essentially all crystal. Barest trace of glass. 



No evidence of dissociation. 



Crystals plus distinct trace of glass. 



80 2CaO.Al 2 3 .Si0 2 — 20[(90 3CaO.Al 2 3 .3Si0 2 ) (10 3Na 2 O.Al 2 3 .3Si0 2 ) ] 



Temperature Time Phases 



1100° 2 hrs. Very good, clear crystalline material with large 



coarse laths and bladed spherulites. 

 Ww =1.660 n € =1.650 



1220° 1 hr. Little dissociation shown by interstitial strong 



birefringent material. Fine-grained aggre- 

 gate. 



1270° 1 hr. Crystals plus included minute drops of glass. 



1435° 1 hr. Coarse grained crystalline aggregate plus a little 



interstitial glass, no, = 1.661 ne — 1.653 



1562° y 2 hr. Glass plus trace of crystals. 



1568° % hr. All glass. 



60 2CaO.Al 2 3 .Si0 2 — 40 [ (90 3CaO.Al 2 3 .3Si0 2 ) (10 3Na 2 O.Al 2 3 .3Si0 2 ) ] 



Temperature Time Phases 



1200° 1 hr. Spherulitic fibers and blades, and fibrous and 



ribbed structured grains. Homogeneous single 

 crystal phase. 



no, = 1.653 n e = 1.642 

 1225° 1 hr. Most grains with a trace of glass, some grains 



apparently homogeneous. 



nperature 

 1200° 



! Time 

 18 hrs. 



1415° 



1 hr. 



1490° 



1 hr. 



1500° 



1 hr. 



