For your visual inspection, here are two snail fossils that appear to now consist of pyrite. Found in the Silurian period Louisville Limestone, they might be some sort of Loxonema. Henry Nettelroth (1835-1887) in his 1889 Kentucky Fossil Shells book lists a Loxonema laeviusculum (Hall, 1879) which looks similar.
Images taken with a microscope set to 23x and an 8 mm FOV. I was looking for graptolites but found these fossils instead.
