Your Wikipedia link says: "The word silex was previously used to refer to flint and chert and sometimes other hard rocks." Seems this was a fairly generic word.

Your Wikipedia link says: "The word silex was previously used to refer to flint and chert and sometimes other hard rocks." Seems this was a fairly generic word. According to http://doi.org/10.3764/aja.122.4.0579 http://doi.org/10.3764/aja.122.4.0579 which is the paper this blog post was based on, "The paving stones of Pompeii consist of a heavy, dark basaltic lava stone, which we describe as 'lava stone,' or silex, using the general Latin term. For local travertine stones, we use the common name, 'Sarno limestone.'" One of the authors of the paper wrote a book, The Traffic Systems of Pompeii, which has: "When covered in gravel or created in beaten earth, the surface was calld glarea, but when paved in harder stones, the term silex was applied."