Diopside — Forsterite — Silica. 



211 



the melting-point of diopsicle. There is no appreciable solid 

 solution. When the mixture diopside 95 per cent, forsterite 5 

 per cent is crystallized both forsterite and diopside appear in the 

 product. The very slight lowering of the melting-point is, 

 therefore, not due to solid solution of forsterite in the diopside. 

 An explanation is offered towards the end of this paper under 

 the heading, " Freezing-point Lowering in Silicate Melts." 



Fig. 2. 



(800 



1600 



1400 



CaMgS. 2 O e 



The liquid us for forsterite was not determined above 1552° 

 and the upper part is, therefore, shown as a dotted curve ex- 

 tending to the melting-point of forsterite. The quenching 

 experiments on the system are tabulated below. 







• 



Table II. 







Composition 

 Diopside Forsterite 



Initial 

 condition 



Tempera- 

 ture 



Time 



Result 



90 



u 



85 



10 



u 



15 



crystalline 



! 1386° 

 1389° 

 1389° 



ihr. 

 ihr. 

 ^hr. 



no change 



glass and diopside 



glass, forsterite and 



a 



a 





1391° 



ihr. 



diopside 

 glass and forsterite 



a 



a 





1412° 



Ur. 



glass and forsterite 



80 



20 





1415° 



1448° 



fhr. 



^hr. 



glass only 



glass and forsterite 



10 



u 

 30 





1453° 

 1550° 



|hr. 

 *hr. 



glass only 



glass and forsterite 



60 



u 



40 





1554° 

 1600° 



ihr. 

 ihr. 



glass only 



glass and forsterite 



