flint
n. C / Un. a very hard, grey or black stone. People used it in the past to make tools or to start fires by striking it against steel to make sparks.
n. a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. Historically utilized for the manufacture of lithic tools and for generating sparks through percussion with steel.
He used a piece of flint to start the campfire.
Archaeologists discovered several arrowheads made of flint buried deep within the cave floor.
The survivalist demonstrated how to produce a steady stream of sparks by striking a high-carbon steel striker against the sharp edge of a freshly knapped piece of flint.
Uncountable when referring to the material in general; countable when referring to a specific piece of the stone.