Flint

Flint is a mineral, found in small chunks around the island. It's relatively uncommon, and unlike stones, it can't be mined from rocks.

Its only use is to light campfires and torches, but that makes it more than worthwhile to pick up the first two pieces of flint you see. Starting a fire with flint is always successful, and the flint is not consumed in the process—both of which make it superior to starting fires with bark and a branch. On the other hand, flint is significantly heavier.