The mineral celestine (SrSO4) was converted to strontium sulphide (SrS) using charcoal in a commercial microwave oven. The effects of microwave exposure times (2, 4 7, 10 min) and percentage of excess charcoal (stoichiometric, 50%, 100%) with respect to the stoichiometric amount on the SrS conversion were investigated by the use of X-ray diffractometry, sulphur/carbon analyses and dissolution tests. The experimental results showed that celestine in the mixture starts to react immediately with charcoal by the initiation of microwave heating, and after 10 min of heating SrSO4 converted to SrS at ratios over 97%. (c) 2007 Elsevier Ltd. All rights reserved.