You can see a similar reaction in action when you work with MgO. When preparing starting materials for high P high T experiments on basaltic liquids we typicall

You can see a similar reaction in action when you work with MgO. When preparing starting materials for high P high T experiments on basaltic liquids we typically make mechanical mixtures of simple oxides. MgO is the usual magnesium source, and we always have to calcine the MgO before weighing, as it always takes on CO2 whilst sitting around in the jar. If you put some freshly calcined MgO on some weighing paper on a balance, you can sit there and watch the mass increase as it reacts with CO2 from the air. Alas, too much silica on earth for periclase rocks...