Calcite with Marcasite     Brushy Creek Mine, Oates, Missouri.  Ex. Dr. Steve Chamberlain collection.  A famous find that produced few nice thumbnail sized specimens like this 2.6 x 2.4 x 1.7 cm example.  This piece appears to be a floater.  Very nice.  No damage.  Mounted in a perky box, as seen.   $40