In comparing any mineralization process, it is first important to understand what the source of the calcium or magnesium mineral that is used. Although magnesium hydroxide (Mg(OH)2, brucite) is a natural mineral, it requires mining and processing in order to be used, resulting in a significant carbon emissions: between 400 and 700 gCO2e not including transportation . Thus, any ex-situ mineralization project or process that proposes the use of brucite is inherently a carbon emitter before it has been deployed ). An alternative source of "reactive" MgO is in olivine , a magnesium iron silicate which reacts with atmospheric CO2; however, before use it must be mined, crushed and transported, all of which are energy intensive and result in carbon emissions.