WHEN metallic sodium is added to a eutectic aluminium–silicon alloy, the structure of the eutectic silicon is modified by a mechanism which has been described by several authors1–4. Sodium also modifies the structure of primary silicon crystals in this system, and various workers1,5 have stated that a spheroidal form of silicon can be obtained by this means. Evidence that these spherical particles are true Spherulites has not been provided and I wish to describe some preliminary experiments carried out to ascertain the morphology and possible crystallography of these interesting particles.