Disilicate quartz eutectic

The sodium disilicate-quartz eutectic occurs at 74.2 + 0.3 wt % SiOz and 789°C [8], A metastable eutectic between Na20 2Si02 and tridymite exists at 74.6 wt % Si02 and 782°C. 

MLiquid phase formed at the sodium disilicate-quartz interface above the eutectic melting temperature and worked its way outward. Perforation refers to when the outer sodium disilicate shells were no longer continuous. 

The field of sodium disilicate extends from the quartz-disilicate eutectic to the metasilicate-disilicate eutectic originally located at approximately 62.1 wt % Si02 and 837 1°C. The compound Na20 2Si02 melts congruently at 874 3°C and has several polymorphic forms. There are probably three stable forms in addition to several metastable ones. The high-temperature form melts congruently at 874 3°C. There are rapid reversible transitions at 707 and 678°C. 

---