In the last two books of the work (Books XXXVI and XXXVII), Pliny describes many different minerals and gemstones, building on works by Theophrastus and other authors. The topic concentrates on the most valuable gemstones, and he criticises the obsession with luxury products such as engraved gems and hardstone carvings. He provides a thorough discussion of the properties of fluorspar, noting that it is carved into vases and other decorative objects. The account of magnetism includes the myth of Magnes the shepherd.