10 Morey & Boiven — Melting Potash Feldspar. 



one new crystal phase, in which case it can be treated as 

 a two-component system with relations in every respect 

 analogous to those of the binary compound MgSi0 3 . 



"Fig. 3. 



1800 



1600 



1400 



1200 



1000 



Lc. 



& 



LIQ 



Q--\" 



Or 



& 



Lc 



B 



|R.\ 



/ 



SlO; 



& 



LIQ. 



V 



\C/ 



KAl$i 2 O s io KAl$i 3 8 30 40 50 60 70 80 90 *0 



WT.PER CENT 

 Fig. 3. — Diagram illustrating the melting of orthoclase. 



The compound, KAlSi 3 8 , with which we are here con- 

 cerned, breaks up in this latter manner. At 1170° it 

 forms leucite, KAlSi 2 O , and liquid, and its behavior can 

 be completely described in terms of a diagram in which 

 KAlSi 2 6 and Si0 2 are taken as components, when 

 KAlSi 3 8 (orthoclase) becomes a binary compound of 

 these. In fig. 3 the general form which this diagram 

 must assume is shown. We have accurately determined 

 the temperatures on this diagram only at the composition 

 KAlSi 3 O s . Work is now being carried out on the whole 



