Many people incorrectly believe that the fossils in this stone are Ammonites, an extinct species of mollusks, more closely related to coleoids like Octopus, Squid and Cuttlefish, than to modern shellfish. While Ammonites have been beautifully preserved in fossil beds around the world, they are not responsible for the fossils found in Vatican Stone. Instead, the fossils are of an ancient horn Coral species, Dibunophyllum bipartitum. This species thrived during the Carboniferous Period (359-299 million years ago). This species of Coral looked similar to modern Cup Corals in the Balanophylia genus.
At that time, Great Britain and Ireland were tropical islands, close to the equator, nowhere near their current northerly location. Much of the land was submerged under a shallow sea and covered with a thick bed of coral. What little land was above the sea was a tropical swamp. Towards the end of the Carboniferous Period, the various continents fused into a single super-continent, Pangaea. The British Isles and Ireland were pushed Northward, as well as up out of the water. Mountain ranges were formed, and the remains of the swamps were preserved in what would eventually become coal. Vatican Stone is a remnant of this period. It shows perfect Coral fossils, preserved in a black Limestone.
Vatican Stone has been mined in the county of Durham, in north-eastern England for centuries. The oldest written reference to the stone dates to 1183, in a document which mentions “Lambert the marble cutter of Stanhope.” Just as Vatican Stone is often incorrectly thought to be Ammonites, rather than Coral, it was formerly thought to be a type of Marble, rather than Limestone.