Viscosities of magmatic silicate liquids; an empirical method of prediction

Based on the compilations and calculations of Bottinga and Weill (1972), it has been discovered that viscosities of multicomponent anhydrous silicate liquids can be estimated more rapidly and with equal precision using only four partial molar coefficients of SiO ₂ . The addition of a fifth coefficient extends the method to hydrous compositions with somewhat less precision. Comparisons with experimental data are illustrated for viscosities ranging from the order of one poise to 1013 poises and compositions ranging from "lunar basalt" to terrestrial rhyolites and "hydrous granites of ternary minimum composition". The method does not explicitly consider halogens, or other "volatile" or minor constituents, but semiquantitative effects can probably be estimated; the empirical coefficients can easily be expanded in number or refined in value if need is indicated by experimental or other evidence.