A few weeks ago, I visited a quarry in central Iowa more for the purpose of its well known and beautiful crystals, not it's fossils:
I was told that most of the "vugs" were a result of fossil reabsorbtion and calcite deposition in the void. It was hard for me to comprehend until I started splitting open the few brachiopods that I found. They indeed were crystalized in the middle!! Here is one I split open:
Here is the purpose of my post. The dark item is not anything I recognize. Most of the time "black" turns up in this area, I am told it is fish pieces. Does anyone have a suggestion of what part of a fish this would be, IF it is fish at all??