Actually a survivor of the birth of the terrestrial (rocky) planets: Earth, Venus, and Mars. The asteroid is
Lutetia, a main belt asteroid approximately 100 km across. The image below came from a flyby by ESA's Rosetta spacecraft in July 2010.
A team of astronomers from French and North American universities have studied the unusual asteroid Lutetia in detail at a very wide range of wavelengths to deduce its composition. Data from the OSIRIS camera on ESA's Rosetta spacecraft, ESO's New Technology Telescope (NTT) at the La Silla Observatory in Chile, and NASA's Infrared Telescope Facility in Hawaii and Spitzer Space Telescope were combined to create the most complete spectrum of an asteroid ever assembled.
This spectrum of Lutetia was then compared with that of meteorites found on Earth that have been extensively studied in the laboratory. Only one type of meteorite - enstatite chondrites- was found to have properties that matched Lutetia over the full range of colours.
Enstatite chondrites are known to be material that dates from the early Solar System. They are thought to have formed close to the young Sun and to have been a major building block in the formation of the rocky planets, in particular the Earth, Venus and Mercury. Lutetia seems to have originated not in the main belt of asteroids, where it is now, but much closer to the Sun.
OK, so how did Lutetia get from the inner solar system, where the terrestrial planets formed out to the asteroid belt?
Over the last few decades, astronomers have found that the young solar system was more dynamic than previously thought. Near encounters with one of the rocky planets may have ejected Lutetia from the inner solar system; Jupiter's gravitational influence may have also played a part.