The nephelines that crystallize from compositions in the system Na
2O-Fe
2O
3-Al
2O
3-SiO
2 are solid solutions containing Fe
3+. The present study was carried out in order to reveal the nature of the nephelines in this quaternary system. Phase diagram of the join nepheline-Fe
2O
3•3Al
2O
3•6SiO
2 passing through the part poor in Na
2O and Fe
2O
3 in the quaternary system was determined. Unit-cell dimensions of the nephelines in this join indicate that these nephelines contain rather small amount of Fe
3+. On the other hand, the nephelines in the joins nepheline-“iron nepheline (NaFe
3+SiO
4)” and nepheline-acmite, both passing through the part rich in Na
2O and Fe
2O
3, contain significant amount of Fe
3+. From these results it seems that amount of Fe
3+ in the nepheline depends upon bulk composition of starting material, especially contents of Na
2O and Fe
2O
3.
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