Rates of crystallization of Li2O · 2SiO2, from an Li2O · 4SiO2glass as a function of platinum concentration at 600° and 650° C were determined. At both temperatures a maximum rate was obtained in the region of 0.005% Pt. Calculations of the activation energies for the crystallization process showed that 0.005%, Pt lowered it to less than half its original value of 120 kcal per mole. Electron microscopy of this glass quenched from 1450OC revealed a granular structure 250 A in size which was believed to be due to lithium‐rich clusters in the glass, svpporting the concepts of other investigators. In glasses containing 0.025%, an additional phase identified as silica O was found. Explanations for the effectiveness of platinum as a nucleating agent in this glass are of