Editing Natural History (Pliny) (section)

===Mineralogy===

[[File:Intaglio Nero CdM.jpg|thumb|upright|[[Amethyst]] [[Intaglio (jewellery)|intaglio]] (1st century AD) depicting [[Nero]] as [[Apollo]] playing the lyre ''([[Cabinet des Médailles]])'']]

In the last two books of the work (Books XXXVI and XXXVII), Pliny describes many different [[mineral]]s and [[gemstone]]s, 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 gem]]s and [[hardstone carving]]s. He provides a thorough discussion of the properties of [[fluorspar]], noting that it is carved into vases and other decorative objects.<ref>''Natural History'' XXXVII:18-22</ref> The account of magnetism includes the myth of [[Magnes the shepherd]].

Pliny moves into [[crystallography]] and [[mineralogy]], describing the [[octahedral]] shape of the diamond and recording that diamond dust is used by gem engravers to cut and polish other gems, owing to its great [[hardness]].<ref>''Natural History'' XXXVII:55-60</ref> He states that [[rock crystal]] is valuable for its transparency and hardness, and can be carved into vessels and implements. He relates the story of a woman who owned a ladle made of the mineral, paying the sum of 150,000 [[sesterces]] for the item. Nero deliberately broke two crystal cups when he realised that he was about to be deposed, so denying their use to anyone else.<ref>''Natural History'' XXXVII:23-29</ref>

Pliny returns to the problem of fraud and the detection of false gems using several tests, including the scratch test, where counterfeit gems can be marked by a steel file, and genuine ones not. He refers to using one hard mineral to scratch another, presaging the [[Mohs hardness scale]]. Diamond sits at the top of the series because, Pliny says, it will scratch all other minerals.<ref>''Natural History'' XXXVII:196-200</ref>