The Morrison Formation, a geological part of the jurassic periode is given 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. 

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Northamerica/USA/Utah/ agatized Dino Bones, Morrison Formation

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Utah Dino Bone 50mmam
Utah Dino Bone 54mmam
Utah Dino Bone 67mmam
Utah Dino Bone 70mmam
Utah Dino Bone 84mmam
Dinobone utah 145mmam