Ferguson and Merwin — The Ternary System. 99 











Time 







Composition wt. % 



Temp. 



in 



Phases present Boundary 



CaO 



MgO 



Si0 2 



°C. 



min. 







34 



22 



44 



1445 

 1442 



30 

 30 



Glass 



Glass + 2CaO.Mg0.2SiOo -f 



CaO.MgO.SiOa 



8, 9 



39 



18 



43 



1444 

 1429 



20 

 90 



Glass + 2CaO.Mg0.2Si0 2 

 No 2CaO.SiO, 





38 



20 



42 



1436 



20 



No 2CaO.Si0 2 





33 



22 



45 



1432 



1428 



20 

 15 



Glass 



Glass + 2MgO.SiO, -f 



2CaO.MgO.2SiO, 



4, 9 



32 



23 



45 



1430 

 1423 



20 

 15 



Glass -f 2MgO.Si0 2 

 Glass -f 2MgO.Si0 2 -f 



2CaO.Mg0.2Si0 2 





31-5 



22 



46-5 



1410 

 1406 



30 

 25 



Glass + 2MgO.SiO, 

 Glass -f 2MgO.Si0 2 + 



2Ca"O.Mg0.2Si0 2 





30 



22 



48 



1415 

 1392 



20 

 30 



Glass + 2Mg0.Si0 2 



Glass + 2MgO.SiO, -f trace 



2CaO.MgO.2SiO, 





34 



25 



41 



1502 

 1510 



30 

 20 



Glass + MgO -f CaO.MgO.Si0 2 

 Glass -f MgO 



10, 11 



35 



25 



40 



1511 

 1516 



15 

 15 



Glass -f- MgO + CaO.MgO.SiO, 

 Glass -j- MgO 





38 



21 



41 



1489 

 1493 



15 

 15 



Glass 4- 2CaO.SiO, + 



CaO.MgO.SiO, 

 Glass 



8, 10 



40 



22 



38 



1537 



30 



Glass 4- MgO 4- trace 



2CaO.SiO, 



10, 12 



44 



21 



35 



1660 

 1690 



15 



30 



Glass 4- MgO 4- 2CaO.Si0 2 

 Glass 4- trace MgO 4- trace 



2CaO.Si0 2 





31-5 



27 



41-5 



1529 

 1522 



20 

 15 



Glass 



Glass 4- MgO 4- 2MgO.Si0 2 



11, H 



- The similarity between the optical properties of the 

 monticellite crystals which contain in solution some for- 

 sterite and the forsterite crystals themselves is very 

 marked, and for this reason the melting temperatures 

 along the boundary line 9,11 in fig. 8 could not be deter- 

 mined except by the slope of the liquidus of the adjacent 

 fields. 



The Quintuple Points. 



Fourteen quintuple or invariant points at which three 

 crystalline phases and a liquid can co-exist are to be 

 found in this ternary system, and of these, six are true 

 eutectics. These quintuple points are the points of inter- 

 section of three boundary lines and when the tempera- 

 tures along each of three lines fall as they approach the 

 point of intersection the point is called a eutectic. 



Point 1, fig. 8, is a eutectic between diopside, tridy- 



