The cone-in-cone structures form in sedimentary environment.The specimen pictured appears to be from the Coral Ridge Member of the New Providence formation of Bullitt County, Kentucky USA. It formed in the Early Mississippian Period (Osagean). Known as "beef rock" in the British Isles since it looks like a slab of roast beef.
Specimen from the estate of Dr. James Conkin (1924-2017). No label provided so identification is an educated guess. Dr. Conkin first described this structure in 1957 at the Coral Ridge site. He described it as "This double cone-in-cone occurs as two layers of inverted cone-like "golf tees" surrounding an essentially undisturbed solid central mass of impure siderite (FeCO3). These double cone-in-cones occur as elongated lenses embedded in the olive-gray, shale in the upper part of the Coral Ridge Member, approximately 20 feet of the lower New Providence Formation." This layer is associated with "marcasitized megafossil fauna (with goniatite cephalopods, blastoids, "pleurotomarid type" Bembexia ellanae snails, clams, trilobite Philibole conkini ... and the worm burrow Scalarituba missouriensis".
Learn more here: https://en.wikipedia.org/wiki/Cone-in-cone_structures
