organic magnesium salt magnesium carbonate Codex::504 A magnesium salt with formula CMgO3. Its hydrated forms, particularly the di-, tri-, and tetrahydrates occur as minerals. Codex::504(i) A magnesium salt with formula CMgO<small>₃</small>. Its hydrated forms, particularly the di-, tri-, and tetrahydrates occur as minerals. Europe::504 LanguaL term definition: Food additive; technological purpose(s): acidity regulator, anticaking agent, colour retention agent. magnesium carbonates magnesium salt carbonate salt one-carbon compound food additive