What is flint made of?

There are two different flints. One is natural rock (used in flintlock firearms) The other is the "flint" in a cigarette lighter. That is not truly flint, but Misch metal, composed of iron oxide and rare earth metals, such as cerium and neodymium.

Flint is commonly referred to as a quartz mineral, although flint that sparks may be another type as shown above.