118 Ferguson and Merwin — The Ternary System. 



(1) 1-6332 1-639 



(2) 1-631 1-638 



We have been unable to prepare a compound or solid 

 solution having more nearly the formula 8Ca0.4MgO. 

 9Si0 2 . The compound 2CaO.Mg0.2Si0 2 , as far as we 

 know, forms no appreciable solid solutions. 



In this connection attention may be called to the con- 

 fusion which may arise from the use of such formulas as 

 4R"0.3Si0 2 applied to minerals. For the sake of sim- 

 plicity let us assume that we have a case in which B/'O 



Fig. 15. 



1500,. 1500 



1450 _ 



1400 _ ^^ - 1400 



1350 _ -«350 



1300 _ -1300 



C a 0M,0-2Si0 2 2C«0M<30-2Si0i 



Fig. 15.— The binary system CaQ.Mg0.2Si0 2 -2CaOMg0.2Si0 2 . wt. per cent. 



represents but two oxides. 49 As so used R" may repre- 

 sent any one of three things: either (1) two elements in 

 a definite ternary compound; or (2) two elements in solid 

 solutions containing no ternary compounds, but only 

 component oxides and binary compounds, or binary com- 

 pounds alone ; or (3) two elements in solid solution involv- 

 ing ternary compounds, either alone, or with binary 

 compounds, or with component oxides or with both. 



The tridymite-cristobalite inversion. 



The tridymite-cristobalite transformation is very slug- 

 gish even when it takes place through solution. Fenner 50 



49 Similar statements would apply to minerals containing more than three 

 components, but with additional complications. 



50 This Journal (4), 36, 331, 1913. 



