Doctor Who and the Hand of Fear — Terrance Dicks

When the TARDIS lands on Earth in a quarry, the Doctor and Sarah are caught in a mining explosion. She is found clutching what appears to be a fossilised hand, buried in a 150-million-year-old stratum. Analysis shows the hand to be silicon-based and inert, but when Sarah begins to act as if possessed, the Doctor suspects that it may still be alive...