Ferrocerium is an alloy of mischmetal with iron. Mischmetal is formed by extracting all of the rare earth metals except for thorium and electrolyzing their molten chlorides. An alloy of most of the rare earth metals in varying proportions is formed. Ferrocerium is bright silvery gray but forms a black oxide coating which tends to prevent further oxidation in a dry environment. In a wet environment, however, ferrocerium is rapidly and completely corroded. When scraped, ferrocerium makes small shavings of highly pyrophoric metal that are used in cigarette lighters and firestarters because the sparks burn very hot.
Ferrocerium dissolves readily in acetic acid to form cerium and lanthanum acetate. Most of the iron accumulates as powder. However, due to dissolved oxygen, some iron dissolves, contaminating the rare earth solution. There are good ways, but I have not successfully separated the iron from the rare earth metals in solution.
Ferrocerium reacts with warm water, forming hydrogen gas and a mixture of metal hydroxides. This reaction is similar to magnesium. The coating of hydroxides is slimy and grayish.
Ferrocerium also burns in air. The formation of black iron(II,III) oxide as well as cerium and lanthanum oxides make the resulting product dark grayish-black.
See Firestarter Business for more information and a video about ferrocerium reaections.