Abstract
Blue sodalite Na sub(8)(Al sub(6)Si sub(6)O sub(24))Cl sub(2) shows a single isotropic electron spin resonance line at g = 2.011. The resonance is attributed to conduction electron spin resonance of colloidal, small-size, sodium metal clusters. The process of aggregation of sodium and the general behavior of the isotropic line are discussed with reference to some of the postulated mechanisms.