en.wikipedia.org/wiki/Carbon_planet
www.cosmosmagazine.com/features/print/2914/weird-worlds
“Built out of relatively more carbon than oxygen, such a planet would still have a metallic iron core, but the outer layers could be composed of ceramics – silicon and titanium carbides – with a shell of pure carbon on top.
These ceramics and graphite would make the entire planet extremely hard and heat-resistant, and it could survive much closer to its star. Even more bizarre is that the high pressure beneath the surface would convert the bottom of the graphite layer into an entire shell of diamond that would be many kilometres thick.
The surface of such a gem planet would be equally alien looking. The atmosphere would likely be rich with carbon monoxide and methane, which would react in the sunlight to turn the skies hazy with hydrocarbons. Long-chain hydrocarbons would condense into clouds and fall as rain, filing the oceans with oil and smearing the ground with sludgy tar. ”
Last 3 pics are of one such (fictional) world, “Narshad”:
www.solarvoyager.com/forum/forum_posts.asp?TID=4748
