The heat capacities of eight chlorine boracites T3B7O13Cl (T=Cr, Mn, Fe, Co, Ni, Cu, Zn or Mg) have been measured in the temperature range 2 to 100 K. Magnetic phase transitions occur below 20 K in the compounds studied except in the two non-magnetic substances Zn3B7O13Cl and Mg3B7O13Cl. The magnetic specific heat capacities give information on magnetic ground state of the transition metals and the entropy related to the phase transitions.