The dewetting behavior of vacuum deposited CsI films on LiF (1 0 0) oriented substrate was observed. Rupture of initially continuous solid films occurs in a duration of months-minutes, depending on film thickness. Finally, spherical particles are formed on the substrate. The particles possess a pronounced orientation in the < 1 1 0 > direction normal to the substrate surface. This effect has been attributed to the difference between surface energy values of the film and substrate, and the interface energy according to Young's equation. The corresponding values of surface energy have been calculated and have confirmed the nature of the observed effect. (C) 2010 Elsevier B.V. All rights reserved.