flint

a hard kind of stone; a form of silica more opaque than chalcedony

a river in western Georgia that flows generally south to join the Chattahoochee River at the Florida border where they form the Apalachicola River

a city in southeast central Michigan near Detroit; automobile manufacturing

showing unfeeling resistance to tender feelings; "his flinty gaze"; "the child's misery would move even the most obdurate heart"