The apolar (Lifshitz van der Waals)component (yLW) and the polar [electron-acceptor (y ) and electron-donor (y ) ] parameters of the surface tension of more than sixty different clay and other mineral particles or surfaces have been measured, as well as their -potentials. It is essentially the y parameter that determines the hydrophobic (target;⩾y28 mJ/m1)or hydrophilicy ( ytarget;⩾28 mJ/mJ) character of the mineral surface.