Flint (or flintstone) is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks. American Indians of various tribes extracted the rocks and formed them into arrowheads to make their signature weapons more lethal. Oh, wait, did you mean the city? The seal of the city represents flint arrowheads, automobile manufacturing, and skyscraper-building, none of which are left.