any meteorite containing substantial amounts of both rocky material (silicates) and nickel-iron metal. Such meteorites, which are often called stony irons, are an intermediate type between the two more common types, stony meteorites and iron meteorites. In specimens of one common type of stony iron, known as pallasites (formerly called lithosiderites), the nickel-iron is a coherent mass enclosing separated stony parts. The material that makes up pallasites probably formed, after melting and differentiation of their parent asteroids, at the interface between the nickel-iron metal core and the surrounding silicate mantle. The other common type, the mesosiderites (formerly called siderolites), are impact breccias. They are probably related to the basaltic achondrite group of stony meteorites, but they contain an unusually large quantity of interspersed metal. The source of the metal is not known for certain, but it may be from the core of the body that collided with and brecciated the mesosiderite parent body.