A method of sizing finely ground, insoluble, homogeneous material or classifying ore particles. A weighed quantity is dispersed in liquid and allowed to settle for a timed period, a liquid fraction then being decanted. The treatment is repeated several times, the settled fraction now representing one size group (if homogeneous) or settled group (if minerals of various densities are present). The decanted fluid is similarly treated for progressively lengthened settling periods.