For a natural single crystal of zircon, ZrSiO₄, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of -decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the -decay dose varies between 2 10¹⁵ and 1 10¹⁶ -decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 10¹⁵ to 9.7 10¹⁵ -decay events/mg) both the hardness and elastic modulus decrease linearly with increasing -decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence, hardness and bulk modulus.