The Ternary System MgO-Al^O.-SiO,. 323 



boundary curves. A solid model corresponding to fig. 6 

 is shown in fig. 7, and the structure 9 of the model before 

 filling with plaster can be seen in fig. 8. 



Natural Coedierite. 



So little is known concerning natural cordierite that 

 very definite comparisons between it and the ternary 



Fig. 7. 



compound just described can not be made. The ternary 

 compound has been called cordierite for various reasons 

 which appear in the text, but which need not be enu- 

 merated here. Possibly as much as 2 or 3 per cent of 



"For description see The Ternary System CaO-AL0 3 -SiO», this Journal, 

 39, 16, 1915. 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 2G8. — April, 1918. 

 23 



