The compositions disclosed contain a diorganopolysiloxane, a finely divided reinforcing silica filler, a powder of a ferrite such as a divalent metallic element such as manganese, copper, nickel, from 10 to 70 parts by weight of a finely divided inorganic material, such as mica or glass powders, finely divided platinum metal, a curing agent for silicone rubbers such as a peroxide or condensation c