CuI nanocrystals were formed by attrition of Cu and I at ambient temperature. They were characterized by XRD to be zincblende, γ-CuI with an average particle size of 20 – 40 nm. The crystallographic phase transitions from zincblende (γ-phase)-to-distorted wurtzite (β-phase)- to-disordered zincblende (α-phase) were also investigated through non-isothermal DSC. Transition temperatures, enthalpies and entropies of these two-phase transitions as well as their “activation energies” were obtained, treating the phase transitions as “reactions”. It is inferred that attrition imparts a partial cation disorder into CuI, unlike a wet chemical reaction. Attrition essentially prepares the fcc Cu lattice for accommodation of I ions in a weakly covalent arrangement.