Brucite manufacturers answer for you: magnesium hydroxide is heated to produce magnesium oxide and water. Magnesium oxide does not react with water to form magnesium hydroxide. Calcium hydroxide cannot be heated to produce calcium oxide. Calcium hydroxide precipitated by lime water heating does not need to be marked with precipitation symbol. Calcium hydroxide is an alkali, a pure substance, not a liquid! Lime water is an aqueous solution of calcium hydroxide and a mixture.