Location and Uses
Flint can be found after breaking Ore Deposits, Luminous Ore Deposits, and Rare Ore Deposits. Striking pieces of Flint with metal Weapons cause the Flint to ignite. This can be used to create Campfires by dropping a piece near some Wood before striking it. It can be used to relight Campfires, including the Campfires under Cooking Pots, by placing some Flint near the Campfire before striking it.
Strike it with a metallic weapon to generate a spark. This portable fire starter breaks after one use, but it can create a long-lasting flame if you use it near firewood." — Inventory (Breath of the Wild)