My cousin has been extracting fossils from some Carlile Shale Formation matrix. It was found in Grant County, South Dakota, USA. He has been carefully breaking it down to extract the hidden fossil shark teeth. The fossils date to the Cretaceous Period (Turonian). The picture shows two Ptychodus whipplei shark teeth fossils.
Thanks to Kenny for the image.
Info Source:
http://oceansofkansas.com/Ptychodus2.html