The Mazon Creek fossil beds are a deposit with exceptional fossil preservation, located in Illinois. (~307 million years old) biota ranks among the great fossil sites around the world. Fossils from this site are often quite detailed and are preserved within siderite (iron carbonate) nodules. Going Clockwise could be seen Horseshoe crab (Euproops Danae) inside a nodule 5,5x4,5 cm. Essexella asherae (scyphomedusan jellyfish) inside a nodule 4x4 cm. Fossundecima konecniorum worm inside a nodule 5x3,5 cm. Cylcus Americanus, an interesting crabs could be found olly there. it's inside a nodule 3x3,5 cm. All fossils are small but refined. 100% natural with no warnish or brokenings