The ground state magnetic dipole moment of9Chas been remeasured using the &bgr;-NMR technique and our new value of1.396(3)&mgr;Nis in agreement with the previously measured value for this nuclide. The quenched magnetic moment of9Cand the anomalously large isoscalar spin expectation value for the9C−9LiT=3/2mirror pair compare favorably with the results of shell model calculations employing isospin nonconserving (INC) interactions. The ground state magnetic moment of21Mgwas also investigated to determine the significance of INC effects in the heavierA=21T=3/2mirror system. ©1998 American Institute of Physics.