All these fossils were found in the Waldron Shale of Clark County, Indiana. All contain pyrite or marcasite minerals. These first two pictures show the iron sulfide clusters embedded in a Silurian Period brachiopod Homoespirifer evax.
The next two pictures show a segment of byrozoan encrusted with pyrite.
The last two pictures do not this fossil pairing justice. It is a crinoid stem that has another crinoid holdfast wrapped around the stem. Both are encrusted with pyrite or marcasite. A nice photo of one these crinoid ensembles at the Falls of the Ohio State Park web site: CLICK HERE.