The Mazon Creek riverbed is a famous source of fossils set in ironstone, like this fern. The riverbed is nationally protected as a source of valuable paleoecological data, called a konservat-lagerstatte.
 
Weight of entire piece: 62.3 g
 
Measurements: when together, 2.5" x 1.5" x .5"
 
Time Period: mid-Pennsylvanian epoch of Carboniferous period