Cleavage energies of the eleven studied Miller indices, calculated using the Fiorentini-Methfessel approach, all fall in the relatively wide 0.41-2.93 J m -2 range. The relaxed surface energies were up to 1 J m -2 lower compared to the cleavage energies, covering a slightly narrower 0.39-1.99 J m -2 range. The (001) surface was found to be the most stable with a surface energy of 0.39 J m -2 . Only three surfaces, (001), ( ) and (211), appeared on the Wulff construction representing the equilibrium form of Y 2 Ti 2 O 5 S 2 at the thermodynamic limit. Overall, the general plate-like shape with the basal (001) plane agrees well with the reported experimental particle morphology.