210 



JV. L. Bowen — The Ternary System : 



bole, as has been found to be true of the pure magnesian 

 amphibole.** 



The refractive indices are 7 = 1*638 ± '003, a = T620 ± 

 •003. Optical character -f, 2 V about 45°. Occasional mark- 

 ings suggesting the amphibole cleavage of 120° were observed. 



Fig. 1. 



FORSTERITE x 



& \ 



LIQUID 



CRISTOBALITE & LIQUID 



FORSTERITE 



& 



CUNO-ENSTATITE 



CLINO-ENSTATITE & CRISTOBALITE 



M e SiO 





20 MgSi0 3 40 W1 



"PERCENT 8 ° Si0 2 









Table I. 







Composition 

 Diopside Si0 3 



Initial 

 condition 



Tempera 

 ture 



Time 



Eesult 



90 

 n 



a 



10 

 a 



a 



crystalline 1360 

 " 1365 

 " 1375 



1 hr. 

 1 hr. 

 1 hr. 



all crystalline 

 glass and diopside 

 glass and diopside 



u 



a 



a 



1380 



1 hr. 



glass only 



85 



15 



a 



1360 



1 hr. 



all crystalline 



u 



83 



a 

 17 





1364 

 1364 



1 hr. 

 1 hr. 



glass and diopside 

 glass and tridvmite 



80 



20 



It 



1448 



2 hrs. 



glass and cristobalite 



75 



u 



25 





1453 

 1577 



ihr. 

 2 hrs. 



glass only 



glass and cristobalite 



tt 



u 



k 



1583 



|hr. 



glass only 



The System CaMgSi 2 -Mg 2 Si0 4 . 



The system diopside-forsterite also shows the eutectic rela- 

 tion (fig. 3). The eutectic point, at the composition forsterite 

 12 per cent, diopside 88 per cent, is only about 4°-5° lower than 



* Allen, Wright and Clement : Minerals of the Composition MgSiOs, this 

 Journal (4), xxii, 434, 1906. 



