We introduce an instrument and novel method for characterizing the bulk magnetic susceptibility of granular mixtures by submerging an inductor coil in a bed of metallic beads and gauging changes in self-inductance. The resonance frequency of the coil was measured to determine its inductance and evaluate the magnetic permeability of ferrous mixtures relative to air. In air, our coil was accurate to within 0.1% of the permeability of free space. The range of magnetic susceptibility values for magnetically inhomogeneous granular mixtures is poorly constrained, but our coil uniquely quantifies bulk effects that other surface meters are not designed to resolve. Compared to both a commercial Terraplus Inc. KT-10 meter and theoretical approximations, we report similar trends in susceptibility values measured as a function of mass of ferromagnetic material per volume.