In this study, effects of concentration of anionic collectors like KO1, Flotinor FS-2 and modifying reagents like MgCl2, CaCl2, Na2SiO3• 5H(2)O and CMC on surface properties of huntite and hydromagnesite as unusual carbonates have been investigated. The results of microflotation tests have indicated that KO1 is more efficient than Flotinor FS-2. And also, MgCl2, CaCl2 have a negative effect on the flotability of huntite and hydromagnesite. Na2SiO3• 5H(2)O has no significant effect on the flotability of these unusual carbonates. On the other hand, CMC has acted as a depressant on huntite but there is no clear effect on hydromagnesite. © 2004 Elsevier Ltd. All rights reserved.