Sticking to our own solar system for the moment, aside from Earth, where else could we reasonably expect to find diamonds? According the the Columbia encyclopedia: "Diamonds are found in alluvial (loose earthy material deposited by running water) formations and in volcanic pipes, filled for most of their length with blue ground or kimberlite, an igneous rock consisting largely of serpentine." I don't know how common "volcanic pipes" may or may not be on other planets (or moons), but running water seems to be a fairly rare thing in our solar system. How likely is it that Earth is the only place in our solar system where we're ever likely to find diamonds? (At least diamonds on the surface of a planet or moon). I'm working on a story that revolves around an unusually large diamond (larger than any found so far on Earth), being found by a robotic rover on another world, and the efforts to bring it back to Earth. Although this story is more about greed and thieves, I'd hate to start it out with the diamond around which the story revolves being "discovered" on a planet or moon that makes those who know a bit more about science than I groan "Oh geeze! Why did he pick X? You'd never find diamonds there! If only he chosen Y. At least then It'd be possible, unlikely, but at least possible." My initial choice for the place where the diamond was to be found was Titan. Why Titan? 'Cause it makes for a neat sounding title. "Stealing Titan's Heart" with "Titan's Heart" being the name given to the newly discovered precious stone (which only goes to show how writers think :surprised , or don't, take yer pick). Well five minutes of checking around sort of nixed that idea. Apparently Titan is little more than an ice ball with a bit of rock in the center. Not exactly the kind of world where we're likely to ever find a diamond. Better ideas anyone?