A highly anisotropic concerted vacancy mediated mechanism is identified for Cl- transport in chlorapatite. This was revealed in molecular dynamics simulations of stoichiometric and CaCl2 deficient chlorapatite. The mechanism was established within the temperature range 1000-1400 K, with an activation energy of 2.37 +/- 0.07 eV. A considerably lower activation energy is predicted in the CaCl2 deficient material, 0.54 +/- 0.16 eV, due to the availability of Cl- vacancies. The transport process involves the concerted migration of two to four Cl- ions directly along the c axis halide channel and is contrasted with the F- interstitial mechanism shown previously in fluorapatite.