Synthetic single-crystals of zircon [(100) growth surfaces] were implanted at 77K with 540 keV Pb ions with fluences of 3.3 × 1011to 5 × 1015ions/cm2—a dose range that completely spans the crystalline-to-amorphous transition as determined by Rutherford backscattering/ion-channeling measurements. A chemically unzoned, natural crystal [polished (100) section] was similarly implanted. Both the natural and synthetic crystals, as examined by mechanical-properties microprobe (MPM) methods, exhibited an overall radiation-induced softening (70% reduction) and decrease in modulus (42%) through the crystalline-to-amorphous transition. This transition occurs over a narrow range of dose, i.e. 1 × 1013to 1 × 1014Pb ions/cm2. Moreover, below the transition, a pronounced radiation-induced hardening occurs in the near-surface region of the synthetic crystals. This radiation hardening may be due to the accumulation of interstitials. In contrast, the natural zircon showed no hardening; however, its initially higher hardness values suggest that it was already hardened. Despite the continued re-damage process (due to overlapping of displacement cascades) for ion doses beyond the saturation value of 1 × 1014ions/cm2the hardness remains constant.