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I have been watching comments about pyrite for awhile, and have shown my sample, in situ, along with two orthocones that would be nice to identify. they are from a Northern Wisconsin quarry about 15 miles due east of Green Bay. When I first started looking for fossils around my home town, I was told there weren't any because the glacier scraped away the material...since then, i have learned there are fairly large swathes of geology that do contain wonderful fossils...most often found from quarries, where the Glaciers didnt scrap deeply enough to affect them, or from areas possibly missed as in the makoqueta shale near Green Bay. At any rate, what I am interested in is the process by which the pyrite is formed. Does iron seep into the crevice for a fossil was formed, or is the iron actually from the body of the animal itself. For example, in the conesauga shale trilobites ( which are all wonderful by the way) many impressions are surrounded by a circle detail left from gasses that leached into the surrounding area...are these iron oxides from the body of the animal also...and are they therefore considered some form of fossil as well? Thanks for the knowledge, in advance. (the pyrite is about 2 inches across, the deep ridged impression about 6 inch long, and the orthocone about 18". It was my first fossil trip in the area and I had no measuring tools along. The large orthocone was in a block of about 600 pounds or it would have been coming home with me...LOL>