Corundum cristobalite

Stone. A crystalline inclusion present as a fault in glass stones may result from incomplete reaction of particles of batch or from the pick-up of small fragments of the refractory lining of the pot or furnace in which the glass is melted. The most common constituents of stones are carnegieite, corundum, cristobalite, mullite, nephelite, tridymite and zirconia. See also china stone. 

Temp, °C Fireclay Silica Brick Magnesite Chrome Forsterite Mullite Cristobalite Periclase Corundum... 

The primary phase fields that appear on the liquidus surface within the Na20-Al203-Si02 system are cristobalite, tridymite, quartz, sodium disilicates, sodium metasilicate, mullite, corundum, nepheline, carnegieite, albite, and sodium orthosilicate solid solution. 

The two samples comprised of 100% and 80% silica, respectively, formed sodium silicates that melted near 800°C. The authors pointed out that with the sample containing 60% silica—40% alumina, the soda first combined with cristobalite to form sodium silicate and then reacted with the mullite to form nepheline and liberate corundum. 

Dove MT, Keen DA, Harmon AC, Swainson IP (1997) Direct measurement of Si-O bond length and of orientational disorder in the high-temperatuie phase of cristobalite. Phys Chem Min 24 311-317 Duan Z, Moller N, Weare JH (1995) Measurement of the PVT properties of water to 25 kBars and 1600°C from synthetic fluid inclusions in corundum - Comment Geochim Cosmochim Acta 59 2639-2639 Duffy DM and Tasker PW (1986) Theoretical studies of diOhsion-processes down coincident tilt boundaries in NiO. Phil Mag 54 759-771... 

C Crystallization of amorphous silica to cristobalite, formation of corundum, spinels, mullite, Ca silicates, pyroxenes,... 

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