The invention relates to a novel thermodynamically stable crystal modificationof 2-({2-chloro-4-(methylsulfonyl)-3-[(2,2,2-trifluoroethoxy)methyl]phenyl}carbonyl)cyclohexane-1,3-dione.A thermodynamically stable crystal modification of the herbicidal agent 2-({2-chloro-4-(methylsulfonyl)-3-[(2,2,2-trifluoroethoxy)methyl]phenyl}carbonyl)cyclohexane-1,3-dione(Tembotrione) is described. This thermodynamically stable crystal modificationhas particular advantages in the stability of suspension formulations.