M-type asteroids are metallic asteroids; they are moderately bright (albedo .10-.18) and made of nickel-iron, either pure or mixed with stone. They are thought to be samples of the metallic core of differentiated asteroids and originate in the inner portion of the asteroid belt. They have a featureless flat to reddish spectrum.

16 Psyche is the largest M-type asteroid. 21 Lutetia will be the first M-type asteroid to be imaged by a spacecraft when the Rosetta space probe visits it on July 10, 2010. Another M-type, 216 Kleopatra, was the first main belt asteroid to be imaged by radar by the Arecibo Observatory in Puerto Rico.

You can use the "What links here" toolbox link to find more asteroids of this type.