One of the rarest species in Cave-in-Rock is marcasite. Accounts of occurrences are found in old geological publications but these are nearly all from the Rosiclare District and isolated to vein-type ore bodies. Well formed crystals like this specimen shows are exceedingly rare. In addition, there are abundant drusy pyrite and associated calcite. This would be a very fine specimen of zoned yellow and purple fluorite even without the bladed marcasite. Collection of Wayne Fowler: former Vice President and General Manager of Ozark-Mahoning Company 1960-1981. Entered into Ross C. Lillie database as RCL2707.