Calcite single crystals on neutron bombardment change their colour to pale red, red and deep red, as the duration of irradiation increases. The irradiated surface becomes rugged and on etching, a large number of micropits are observed. Using Vicker’s hardness indenter, it is observed that the hardress of the irradiated crystal increases with the increase in the total dosage. From Laue x-ray diffraction studies of irradiated crystals, distortion of lattice is observed. Absorption spectra in the visible region show an extra peak for irradiated samples which is absent for radiated ones. The radiation effects are annealed to a considerable extent on heat treatment. The implications are discussed.