kamacite, mineral consisting of iron alloyed with 5–7 percent nickel by weight and found in almost all meteorites which contain nickel-iron metal. It has a body-centred cubic structure and is sometimes referred to as α iron, after one of the three temperature-dependent forms (allotropes) of pure iron, because the kamacite has the same body-centred cubic structure as α iron. In the iron meteorites, it comprises all the metal in hexahedrites; it also is a principal constituent of the octahedrites, where it is intergrown with taenite, a face-centred cubic nickel-iron mineral.