Morey & Boicen — Melting Potash Feldspar. 7 



Pure synthetic potash feldspar (initially crystalline). 



No change. 



About half changed to glass showing 

 cross-lining (leucite.) 



All changed to glass showing cross-lin- 

 ing (leucite). 



Glass and definite skeletal forms of leu- 

 cite. 



Glass and definite leueites, principally 

 rectangular crosses. 



Glass and minute rounded leueites. 



Glass and rounded leueites (0.02 mm. 

 diameter). 



Glass and rare leueites. 



Glass only. 



Pure synthetic KAlSi 3 O s {initially glass). 



Glass and definite skeletal forms of leu- 

 cite. 



Glass and definite leueites, principally 

 rectangular crosses. 



Glass and minute rounded leueites. 



Glass and rounded to subhedral leueites. 



equal period. The foreign matter apparently lowers the 

 viscosity of the liquid appreciably. Notably typical 

 leucite crystals were obtained by holding the North. Caro- 

 lina microcline at 1400° for 3 days. 



The upper limit of temperature at which leucite crystals 

 are obtained varies greatly in the different feldspars. 

 As is to be expected, the presence of other compounds 

 lowers the temperature of complete melting. Thus the 

 Carolina microcline is all liquid at about 1440°, the sani- 

 dine and adularia at about 1460°, but the pure potash 

 feldspar is not completely liquid until a temperature of 

 about 1530 z is reached. Therefore, between the temper- 

 atures 1170° and 1530°, an interval of 360°, a mass of 

 the composition of pure potash feldspar, KAlSi 3 O s , con- 

 sists, at equilibrium, of leucite crystals and liquid. That 

 we have obtained equilibrium is unquestionable, for we 

 were able to approach it from opposite directions. 

 Whether we started with crystalline potash feldspar or 

 with a glass of that composition we always obtained 



1140 

 1179 



8 days 

 8 days 



1204 



8 days 



1252 



5 days 



1400 



3 days 



1510 

 1510 



2 hrs. 

 20 hrs. 



1525 

 1535 



20 hrs. 

 2 hrs. 





Pure sy 



1252 



5 days 



1400 



3 days 



1510 

 1510 



2 hrs. 

 20 hrs. 



