Rheology of silicates (melts or super cooled as glasses) is one of the most important fields to mankind, as geological activity largely influences life. In this paper, unifying empirical models for the non-Newtonian shear viscosity and the extensional viscosity are proposed. The models have only one parameter, the zero-shear viscosity (the Newtonian plateau), and are valid for a wide range of chemical compositions. (C) 2004 Elsevier B.V. All rights reserved.