The Morrison Formation, a geological part of the jurassic periode is offering in Utah sometimes the possibilitiy to discover dinosaur-fossils (the big theropods are famous - like the apatosaurus). Sometimes the structure of dinosaur-bones is completely replaced by nicely coloured little fortification - agates. This material is one of the most desired for cabochon - cutting. It is sold as “gembone”.  Only in a few cases in the hollow center of the largest bones of a dinosaur ( like the femur or other large leg-bones ) fortification agates in a size of more than 3 cm do occur. Another world famous location for dinosaur bones is situated in the Rio Negro Area in Argentina.