The effect of grinding on the solubility of fluorapatite from the Burenkhaan deposit, Mongolia, has been studied. Mechanical activation distorts the crystalline structure and reduces the particle size, but did not result in the observation of any new crystalline phases. Mechanical treatment increases the solubility of the fluorapatite in citric acid solution from 6% to 17%, suggested to be due mainly to amorphisation of the apatite. (c) 2006 Elsevier Ltd. All rights reserved.