Precise knowledge of the charge and rigidity dependence of the secondary cosmic ray fluxes and the secondary to primary flux ratios is essential in the understanding of cosmic ray propagation. We report the properties of secondary cosmic ray fluorine F in the rigidity R range 2.15 GV to 2.9 TV based on 0.29 million events collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. The fluorine spectrum deviates from a single power law above 200 GV. The heavier secondary-to-primary F/Si flux ratio rigidity dependence is distinctly different from the lighter B/O (or B/C) rigidity dependence. In particular, above 10 GV, the F/Si B/O ratio can be described by a power law R^δ with δ = 0.052 ± 0.007. This shows that the propagation properties of heavy cosmic rays, from F to Si, are different from those of light cosmic rays, from He to O.