An electron-ordering transition occurring in a mixed-valent system that results in an ordering of formal valence states in the low-temperature phase. Example: The prototype system, first identified by Verwey, is the ferrospinel magnetite, Fe³⁺[Fe³⁺Fe²⁺]O₄ in which an ordering of Fe³⁺ and Fe²⁺ ions within octahedral sites is thought to occur below T v ≈ 120 K.