rocky world is composed mainly of carbon (in the form of diamond and graphite), as well as iron, silicon carbide, and potentially silicates.

http://today.msnbc.msn.com/id/49375536/ns/technology_and_science-space/#.UHcEW2_A-3I

The alien planet, a so-called "super-Earth," is called 55 Cancri e and was discovered in 2004 around a nearby star in our Milky Way galaxy. After estimating the planet's mass and radius, and studying its host star's composition, scientists now say the rocky world is composed mainly of carbon (in the form of diamond and graphite), as well as iron, silicon carbide, and potentially silicates.

At least a third of the planet's mass is likely pure diamond.

"This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth," lead researcher Nikku Madhusudhan of Yale University said in a statement. "The surface of this planet is likely covered in graphite and diamond rather than water and granite."