Abstract: This invention is concerned with the recovery of relatively pure magnesia from magnesite which is normally contaminated with too much silica and silicates to permit the magnesite simply to be calcined for the recovery of refractory grade magnesia. The magnesite in its raw uncalcined state is treated with SO.sub.2 at elevated temperatures preferably between 50.degree. and 60.degree. C. thereby rapidly dissolving a high proportion of magnesium as bisulphite without the cost of initial calcination and without dissolving above about 1% of SiO.sub.2 present in the magnesite. The solution of magnesium bisulphite can thus be purified by filtration and magnesia may be recovered in known manner from the purified solution.