Olivine Crystals in a Metal Matrix (IMAGE) Washington University in St. Louis Caption The rusting fusion crust on the outside of the Conception Junction meteorite disguises it as just another rock, but one glimpse of the interior gives the game away. The olive-green crystals set in lustrous metal are unique to pallasites and so unlike anything on Earth that pallasites were the first rocks to be identified as of extraterrestrial origin. Pallasites are thought to come from the core/mantle boundary of differentiated asteroids, the olivine form the mantle and the metal from the core. Credit Dave Gheesling Usage Restrictions Appropriate caption and credit required License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.