490 Bowen and Andersen — Binary System MgO-SiO^ 



Composition 

 Oxides Compounds 



Tempera 

 ture 



Time 



Result 



MgO Si0 2 ( MgSiOs 97-5 ) 

 39 61 \ Si0 2 2-5 \ 



1558° 

 1556° 



1 hr. 



1 hr. 



glass only 



glass and clino-enstatite 



N * 60-8 \«g°- »* f 



1560 n 



1558° 



1 hr. 



1 hr. 



glass only 



glass and forsterite 



Composition = MgSi0 3 97'5#, Si0 2 2-5£ 



(d) Temperature and Composition of Eutectic 

 Clino-enstatite-Cristobalite. 



MgO Si0 2 ( MgSi0 3 90 ) 1540° 2 hrs. Clino-enstatite and cristo- 



[ balite 



36 64 ( Si0 2 10 ) 1545° 2 hrs. Clino-enstatite and glass 



iMgSi0 3 87 - 5 ) 1542° 2 hrs. Clino-enstatite and cristo- 

 [ balite 



Si0 2 12-5 ) 1544° 2 hrs. glass only 



( MgSi0 3 75 ) 1540° 2 hrs. Clino-enstatite and cristo- 

 30 70 \ balite 



( Si0 2 25 ) 1545° 2 hrs. glass and cristobalite 



Temperature = 1543° ± 2° 

 Composition = MgSiOs 87-5<£, Si0 2 12*5^ 



(e) Liquid of Clino-enstatite. 



MgO SiO, j MgSiOs 97 ) 1557° 1 hr. glass only 



38'8 61'2 I Si0 2 3 f 1555° 1 hr. glass and clino-enstatite 



qfi RA i M g Si °3 90 ) 1554° 2 hrs. glass only 



rf0 °* I Si0 2 10 J 1550° 2 hrs. glass and clino-enstatite 



Observed in Iridium Furnace. 

 Temperature Measured with Optical Pyrometer. 



Oxides Compounds Temperature 



MgO Si0 2 Mg 2 Si0 4 100$ melting point 1890° ± 20° 



57-2 42-8 



65 35 -j So iC>4 14 \ eutectic melting 1850° ± 20° 



Summary of Invariant Points.* 



Solid Phases Liquid Phase Temperature 



Periclase (MgO) MgO 100 % 2800° (Kanolt) 



< Periclase (MgO) ) j < 14* MgO \ 185Q o 9Q o 



\ Forsterite (Mg 2 Si0 4 ) J \ > 86$ Mg 2 SiO*) \ ° U ± ~ U 



Forsterite (Mg 2 Si0 4 ) Mg 2 Si0 4 100 % 1890° ± 20° 



S Forsterite (Mg 2 Si0 4 ) ) j MgSiOs 97"5* ) 1W , , „. 



I Clino-enstatite (MgSi0 3 ) ] j Si0 2 2-5$} 100/ ± a 



{ Clino-enstatite (MgSi0 3 ) ) j MgSi0 3 87-5* ) 1 ,,,, * 9 „ 

 } Cristobalite (Si0 2 ) \ { Si0 2 12*5* J ° 6 ± 



Cristobalite (SiO a ) Si0 2 100 % 1625° (Fenner) 



* These points are, of course, invariant only when the system is considered 

 as a condensed system. 



