reduction can be used as an indicator, since the others
contain some iron as part of their chemical composition.
In order to detect changes due to the removal of surface coatings by sonication, we adapted the dynamic contact angle (capillary rise) method of Ayala et al. [6 ] to detect changes in hydrophobicity of the mineral surfaces. Some of the samples were also tested at the Julius Kruttschnitt Mineral Research Center at the University of Queensland, where they have refined the method of Lawver and Wright [7] for measuring resistiv- ity of packed beds of granular material. These tests