Abstract: Magnesium oxide, especially suitable for use in basic refractories, is produced from brine or bittern containing magnesium chloride by:(a) adding to the brine or bittern, as a source of MgO and/or CaO, MgO or Mg(OH).sub.2 or calcined magnesite or calcined dolomite or calcined calcite/limestone in such amount that in the case of MgO, Mg(OH).sub.2 or calcined magnesite, the molar ratio of MgO:MgCl.sub.2 is in the range of 1:1.5 to 1:15 (i.e. 0.66:1 to 0.066:1) or, in the case of calcined dolomite, the molar ratio of MgO+CaO:MgCl.sub.2 is in the range of 0.66:1 to 0.05:1, or, in the case of calcined calcite/limestone, the molar ratio of CaO:MgCl.sub.2 is in the range of 0.66:1 to 0.1:1;(b) keeping the mixture at a temperature below 90.degree. C. till a solid mass is formed; and(c) drying the said solid mass at a temperature up to 200.degree. C.The said mass may then be calcined at a maximum temperature of 1200.degree. C. and optionally then briquetted with a binder and fired at above 1400.degree. C.