Rankin and Wright — Ternary Sij stem CaO-Al 2 O z -SiO„. 11 



(2) The compound 5CaO.SAlfi z (CaO 47'8, A1 2 3 52'2) 

 occurs in two forms : I, a stable form ; II, an unstable mono- 

 tropic form. 



I. The stable form melts at 1455° ± 5°. It forms with the 

 compound 3CaO.Al a 3 the eutectic mixture noted above ; and 



Fig. 3. 



2500 



2400 



2300 



2200 



2100 



2000 



1900 



1800 



1700 



1600 - 



1500 



1400 



Ca + Melt 



/ 

 / 



/ Melt 

 / + 



/ Al 2 3 



Ca0.+3Ca0.Al 2 3 



Ca 3 Al l0 

 AI2O3 



CaO 



-12500 



2300 



2200 



2100 



2000 



1800 



1600 



-1400 



3CaQ.AI 2 3 t Ca0.A 2 3 \ Al 2 3 



5CaO.3AI 2 3 3Ca0.5AI 2 3 



Fig. 3. Concentration-Temperature Diagram for the System Lime- Alu- 

 mina. 



with calcium alumina te a eutectic mixture which has the com- 

 position CaO 47, A1 2 3 53, and melts at 1400° dh 5°. 



The stable form crystallizes in rounded grains without 

 definite crystal outline or distinct cleavage. Luster, vitreous ; 

 fracture, conchoidal and often interrupted ; hardness, 5. 

 Crystal system, isometric ; refractive index, n^= 1*608 ± O'OOl. 



