A new neptunium(V) borate, K[(NpO2)-B10O14(OH)(4)], was synthesized using boric acid as a reactive flux. The compound possesses a layered structure in which Np-V resides in triangular holes, creating a hexagonal-bipyramidal environment around neptunium. This compound is unusual in that it exhibits the Alexandrite effect, a property that is typically restricted to neptunium(IV) compounds.