A sharpened flint for the lock of a gun, to ignite the charge. It was in common use before the introduction of percussion caps.

the piece of flint that provides the igniting spark in a flintlock weapon

Scent of flint sparks in some white wine, eg Pouilly Fum

The taste or smell suggested by wet metal. Often used to describe sauvignon blanc, particularly French ones. Description is a reference to the mineral component in some wines, apparent in the way they taste.