In the production of pure magnesium compounds from serpentinite, acid leaching is usually the first stage of the overall process. However, faster magnesium dissolution can be achieved and the size of a potential leaching reactor can be reduced if serpentinite is calcined prior to leaching. Moreover, use of calcined serpentinite can reduce problems relating to corrosion of the reactor (lower leaching temperatures and pressures can be applied) and foam formation (chemically bonded water, which forms bubbles when released in the reactor, can be removed by calcining). This paper examines how calcination temperature and time influence the amount of magnesium dissolved during the initial period of leaching of calcined serpentine in hydrochloric acid. Fine-grained serpentinite calcined between 640 degrees C and 700 degrees C displayed the highest reactivity. The fraction of magnesium dissolved was up to 30-times higher as compared to leaching of uncalcined serpentine under identical reaction conditions. (c) 2012 Elsevier Ltd. All rights reserved.