Large outcrops of a gemstone mineral commonly used in jewellery have been found on the surface of Mars. On Earth, the mineral olivine takes the form of the brilliant green gemstone peridot. An instrument aboard a Nasa spacecraft spotted a 30,000 square kilometre area rich in olivine in the Nili Fossae region of Mars. The mineral, detected by the Mars Global Surveyor, was exposed on the surface. Scientists believe it might have been thrust up from below the ground by faults and fractures that cover the area. Olivine is abundant in the Earth's outer mantle, the layer just below the...