Flint is a hard stone (see soil types), a form of silica resembling chalcedony but more opaque, less pure, and less lustrous. Tom Stevenson (Sotheby’s Encyclopedia 5th Edition, 2011 p.17-19) describes flint as ‘a siliceous stone that stores and reflects heat and is often associated with a certain “gun-flint” smell  [‘pierre à fusil’] that sometimes occurs in wines, although this is not actually proven and may simply be the taster’s auto-suggestion.’ As well as being used for striking fire flint was also used as a primitive tool or as the core from which such a tool was struck.