The earliest publications on ⁴⁰Ar/³⁹Ar dating recognized the usefulness of ³⁹Ar/³⁷Ar in providing chemical clues to the species releasing argon during stepped heating, while ³⁷Ar measurements are required for interference corrections. Aside from these essential roles, ³⁶Ar, ³⁷Ar and ³⁸Ar have other useful applications. The dominance of Ca as the target nucleus for the production of ³⁸Ar and ³⁶Ar from spallation by cosmic rays has led to the determination of cosmic ray exposure ages from ³⁸Ar/³⁷Ar. ³⁸Ar production from Cl has an important role in the study of ore minerals containing saline fluid inclusions, both in dating and in understanding their genesis. Combining ³⁸Ar/³⁶Ar ratios with micro-thermometric determinations of salinity provides a way to determine absolute concentrations of noble gases in ore fluids. Absorption of cosmic-ray-produced secondary neutrons by ³⁵Cl and ³⁷Cl provides another means to study cosmic ray exposure of meteorites. ³⁶S excesses in meteoritic sodalite provide evidence of now-extinct ³⁶Cl in the early Solar System. Surprisingly, there is little or no evidence of excess ³⁶Ar beyond what can be accounted for by secondary neutron exposure. We have recently devised a method to identify monoisotopic ³⁶Ar from ³⁶Cl decay.