Zircon crystals that have been damaged by a naturally occurring radioactive contaminant, referred to as metamict zircons, have density values ranging from 4.70 to 3.90 g/cm3. The present work is a study of the effect of the damage on the single‐crystal elastic moduli. A systematic and very marked decrease (i.e., up to 69%) of the elastic moduli with density have been observed. All the longitudinal and the shear elastic moduli decrease with radiation damage and approach two common saturation values of 1.5×1012and 0.49×1012dyn/cm2, respectively. Present observation of the elastic moduli of the radiation‐damaged zircon crystals confirms Warren’s theoretical predictions concerning the effect of different pore geometries on the compressibility. Qualitative correlation of the elastic moduli with the structural changes arising from radiation damage in zircon crystals suggests that the marked decrease of the elastic moduli in the radiation‐damaged zircons is caused by the nonspherical defect clusters, microcracks, and pores generated during radiation damage. Thermal annealing, x‐ray diffraction, elastic moduli, and density measurements on the zircon samples confirm the ’’three‐stage’’ process proposed for the metamict transformation of zircons, but the final product of metamictization does not seem to be a mixture of ZrO2and SiO2crystallites.