In summary, ferrite cores by themselves (not including conductors or other additional materials added) should not fail over time. Ferrites are a type of ceramic made from metal oxides, so they will not rust and they will not melt unless exposed to temperatures in excess of 1,000ºC. Ferrites can crack or break due to thermal shock. Ferrites are rather hard and brittle; they can also break or crack upon mechanical impact. If the core has a severe crack perpendicular to the magnetic path, it can cause significant reduction in permeability/inductance or impedance.