Phyllosilicate minerals have been shown to present some rheological challenges during ore beneficiation, with difficulties such as reduced flotation rates and complex tailings treatment arising. This study focuses on two phyllosilicate minerals which commonly exist as major gangue components in many industrial ores: muscovite with its thin platy structure and vermiculite which exhibits concertina-like swelling behaviour. The surface charge distribution of the minerals is evaluated using electrokinetic zeta potential measurements and potentiometric titrations. Rheology tests give the plastic viscosities and Bingham yield stresses of the suspensions. The results show that muscovite and vermiculite particles have an apparent negative charge due to the high aspect ratio of the negatively charged tetrahedral faces to the edges within a tetrahedral-octahedral-tetrahedral (T-O-T) layer configuration. The charge separation between the edges and faces results in the non-typical stacking behaviour of muscovite and vermiculite particles, forming suspensions with higher Bingham yield stresses than quartz, a non-phyllosilicate isotropic mineral with a regular non-platy morphology. However, upon yielding, these structures are destroyed and the resultant suspensions are characterised by low Bingham viscosities similar to isotropic minerals. This study provides a preliminary understanding of the flow behaviour of muscovite and vermiculite. (C) 2011 Elsevier Ltd. All rights reserved.