Rankin and Wright — Ternary System CaO-Al 2 3 -Si0 2 . 5 



the compound 3CaO.Si0 2 . Several of these compounds appear 

 in more than one crystal modification. The temperature con- 

 centration diagram of this binary system is given in fig. 1. 



Calcium metasilicate CaO.Si'O, (CaO 48*2, Si0 2 51 -8) * This 

 compound appears in two distinct forms : (1) the mineral wol- 

 lastonite (/3CaO.SiO Q ), which is found especially in limestone 



Fig. 1. 



CaO.Si0 2 f 2CaO.Si0 2 \ 



3Ca0.2Si0 2 3CaO.Si0 2 



Fig. 1. Concentration-Temperature Diagram for the System Lime-Silica. 



contact metamorphic aureoles and is stable up to 1200°, the 

 reversible inversion point ; (2) pseudowollastonite (aCaO.SiO,), 

 which has never been observed in nature but only in artificial 

 melts and slags ; it is the stable form between 1200° and its 

 melting temperature, 1540° ± 2°. Pseudowollastonite takes up 

 about 2 per cent of either lime or silica in solid solutions ; these 

 additions affect the inversion point, the lime lowering it to 



* All compositions are in weight percentages unless it is expressly stated 

 otherwise. 



