1SS Ferguson and Merwin — The Ternary System. 



tallized at temperatures below the temperature region 

 at which these phases were stable. Thus we found pseu- 

 dowollastonite in ternary compositions which should 

 have been pure wollastonite or 5Ca0.2Mg0.6Si0 2 solid 

 solutions ; binary compositions near the composition 

 3Ca0.2Si0 2 contained some calcium orthosilicate; and 

 the ternary composition corresponding to the compound 

 CaO.MgO.Si0 2 (monticellite) invariably gave not a pure 

 homogeneous product but a mixture of a monticellite 

 solid solution and calcium orthosilicate. 



Recapitulation. 



The stud}; of the ternary system ^ CaO-MgO-Si0 2 24 

 brought to light many perplexing liquidus relations for 

 which there was no adequate explanation. An investi- 

 gation of the solidus relations was therefore started in 

 order to clear up the doubtful points and the results of 

 this investigation are given in this paper. The salient 

 features of these results are: 



(1) A confirmation of the earlier work in regard to 

 the wollastonite-diopside solid solutions, wollastonite 

 taking up a maximum of 17 per cent of diopside. 



(2) The existence of solid solutions of pseudowollas- 

 tonite and diopside containing as a maximum about 16 

 per cent of diopside. 



(3) The finding of the new compound 5Ca0.2MgO. 

 6Si0 2 . 



(4) The existence of solid solutions of akermanite (or 

 perhaps of an unstable compound 3CaO.Mg0.3Si0 2 ) in 

 wollastonite and pseudowollastonite. The wollastonite 

 solutions extend to a composition containing between 60 

 and 70 per cent of akermanite, while the pseudowollasto- 

 nite solutions extend to a composition containing about 

 23 per cent of the same compound. 



(5) The presence of an area of solid solution which 

 includes the wollastonite-diopside, the wollastonite-aker- 

 manite, and the wollastonite-5Ca0.2Mg0.6Si0 2 solid 

 solutions. The decomposition temperatures on this area 

 between the 17 per cent diopside solid solution and the 

 compound 5Ca0.2Mg0.6Si0 o pass through a minimum. 

 5Ca0.2Mg0.6Si0 2 decomposes at 1365°C and the 17 per 

 cent diopside solid solution at about 1340° C, while pure 

 wollastonite inverts at 1200 °C. 



24 This Journal, August number, 1919. 



