抄録
The Cr-bearing silicate systems have a wide liquidus surface for chrome spinel, indicating that a small amount of Cr causes the presence of chrome spinel which gives a significant effect on phase relations in the silicate system. The behavior of chrome spinel is examined by the addition of a small amount of Cr (0.16-0.40 wt% Cr2O3) to the joins CaMgSi2O6-CaAl2Si2O8-Mg2SiO4 and CaMgSi2O6-CaAl2SiO6 in the form of MgCr2O4 and CaCrAlSiO6, respectively. The liquidus surface for chrome spinel expands considerably with the small increase in Cr content of the bulk composition, and liquidus phase relations in the both joins are significantly changed. The spinel phase with very high Cr content (40-50 wt% Cr2O3) is crystallized from melt with very low Cr content. The Cr content of the spinel phase increases with increasing that of bulk composition at 1 atm. The Cr content of spinel phase increases considerably (up to 70 wt% Cr2O3) with increasing pressure when excess water is present, and decreases with decreasing water content of host melt.
