A rod shaped metal alloy containing rare earth elements that can easily produce sparks when struck or grinded. The alloy is sometimes called mischmetal. It may contain iron, carbon, aluminum, and magnesium in addition to the rare earth elements. Although it serves the same purpose as flint, it does not contain any of that mineral. There are many different possible formulations.
This same material is often sold in the form of a larger rod as a "hot spark" or "metal match" for survival kits. They are durable, absolutely waterproof, very easy to use, and can be re-used hundreds or even thousands of times before they wear out. Some are small enough to fit on a keychain. If you spend a lot of time in the outdoors, keeping one there would be a great idea.
They can be used to light a fire even after the butane or lighter fluid has run out. The sparks that they produce are hot enough to ignite a cotton ball, dryer lint, dry grass, flammable liquids, or other good spark catchers. If you have enough free time, an empty cigarette lighter is almost as useful as a full one.
Keychain Metal Match