  The rheological properties of suspensions containing high solid fractions are
investigated. Attention is focused on viscosity of silicate and magmatic melt
systems. A general empirical equation which describes the relative viscosity of
suspensions as a function of suspended solid fraction is proposed. In the limit
of very dilute solid concentrations it reduces to the Einstein equation. The
proposed relationship is satisfactorily applied to reproduce available
experimental data relative to silicate melts. Moreover, the extrapolation of
the model to very high concentrations is compared with experimental
observations on partially-melted granite.
