Particles found floating in ­vials of a fertility drug that was recalled last week by a Waltham speciality pharmacy have been identified as apparently harmless pieces of the vial’s rubber stopper.

Laboratory results given to the Globe late Thursday by ­Village Fertility Pharmacy, which commissioned the ­report, concluded: “The ­vials contained numerous particles that contain polyisobutene with substantial amounts of talc and silica. This composition is typical of rubber stopper formulations.”