Iron-doped zircon (zirconium silicate) has been prepared from silica, zirconia and iron(II) sulphate heptahydrate using a mixture of sodium halides and alkali metal nitrates as mineralisers to lower the temperature of reaction. The formation of a silicon- and fluorine-containing glassy phase in the reaction vessel, together with evidence for a SiF3 breakdown product and the analysis of solid phases formed at intermediate temperatures, implicate the participation of a volatile silicon fluoride intermediate, probably SiF4, in the formation of the iron-doped zircon.