Summary: X-ray, density, refractive index, and optical absorption measurements have been made on metamict Ceylon zircons. The appearance of a previously reported anomalous optical absorption spectrum in low Ceylon zircons has been associated with small particles of cubic or tetragonal zirconium dioxide in a radiation-damaged zircon lattice, in both heated and unheated stones. No evidence of a previously reported second phase was detected in intermediate Ceylon zircons.