Primary crystallization field of cuspidine (3CaO·2SiO2·CaF2) has been experimentally determined in the 2CaO·SiO2-SiO2-CaF2 system by quenching method and differential thermal analysis (DTA). Hermetically closed platinum capsules were used as a sample container to prevent fluorine loss in the form of HF and SiF4 by reaction of CaF2 with moisture or SiO2 for quenching experiments. Combining the present study with the partial phase diagrams previously reported, the whole phase diagram of the CaO-SiO2-CaF2 system has been developed. Cuspidine equilibrates with (2CaO·SiO2)2CaF2, CaO·SiO2, 3CaO·2SiO2, 2CaO·SiO2 and CaF2 in solid state. Cuspidine coexists with liquid phases at temperatures between 1387 K and 1680 K.
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