:>44 Vat/ and Soxinav — Mcltiiuj Point* of Mineral* 

 Fig. l. Fig. 2. 



Fig. 3. 



Fig. 4. 



Fig. 1. Chemically pure diopside. Element E, 14100 microvolts = 1888°. 

 Time, 1 hour. Crossed nicols. 200 diameters. Crystalline. The interfer- 

 ence colors show in bands around the edges of the crystal fragments. 



Fig. 2. Chemically pure diopside. Element R, 14200 microvolts = 

 1396°. Time, 34 hour. Photo with crossed nicols. Magnified 32 diameters. 

 Glass. 



Fig. 3. Chemically pure anorthite. Element R, 15950 microvolts = 1547°. 

 Time, % hour. Crossed nicols. 200 diameters. Crystalline. The twin- 

 ning shows distinctly. 



Fig. 4. Chemically pure anorthite. Element R, 16100 microvolts = 1561°. 

 Time, % hour. Crossed nicols. 100 diameters. Glass. 



temperature, The pure soda feldspar (albite), if held at a tem- 

 perature slightly above its melting point for a sufficient length 

 of time, will melt completely ; the mixture, on the other hand, 

 if held at a temperature within its melting interval, will melt 

 in part, come to equilibrium, and remain indefinitely part crys- 

 talline and part liquid. 



