Viscosities of melts in the Na2O---FeO---Fe2O3---SiO2 system and factors controlling relative viscosities of fully polymerized silicate melts

Na2O---B2O3---SiO2 and Na2O-Ga2O3 viscosities decrease in the order aluminosilicate > ferrosilicate, (galliosilicate ?) > borosilicate. Thp electronegativities of the trivalent cations are inversely correlated with the relative viscosities of melts in these systems. Similarly, the electronegativities of network-stabilizing cations are inversely correlated with melt viscosity for alkali and alkaline-earth aluminosilicate melt systems. The variation in the viscosity of tectosilicate melts is correlated with estimated average T-O-T bond angles, and exothermic heats of solution of quench glasses. Structural controls of viscosity discussed are tetrahedral ordering and relative bond strengths. The acmite component in natural, peralkaline, silicic volcanics will not contribute directly to high melt viscosities for these lavas