Around Wonsheim agate-collectors are able to find in a marine miocaene-aged sediment (called “Dinotheria-Sand”) some specimen of distinctive agates. This sediment by one long past sea forwards in the area of the Mainzer basin in the Miocaen was deposited. An eloquent certification for this are the finds of fossils of large sea mammals, that can be made while rockhounding. The agates are strongly waterworn and are showing a grey to white surface. Also in their inside they are usually strongly decolorized. Sometimes nevertheless inside remains a center with colored pigments. Also pseudomorphous formations are found in this region.