Cone-in-cone structures

Cone-in-cone structures are secondary sedimentary structures that form in association with deeper burial and diagenesis. They consist of concentric inter-bedded cones of calcite or more rarely gypsum, siderite or pyrite. Although several mechanisms may be responsible for the formation of cone-in-cone structures, displacive crystal mechanism is preferred. It accounts for the most uniform and consistent explanation of growth and why cone-in-cone can occur with such variable composition. Cone-in-cone structures are secondary sedimentary structures that form in association with deeper burial and diagenesis. They consist of concentric inter-bedded cones of calcite or more rarely gypsum, siderite or pyrite. Although several mechanisms may be responsible for the formation of cone-in-cone structures, displacive crystal mechanism is preferred. It accounts for the most uniform and consistent explanation of growth and why cone-in-cone can occur with such variable composition. Cone-in-cone structures are identifiable by their distinctive conical appearance. They are composed of concentric cones nested inside each other. The actual composition of the cones is variable and dependent on the environment in which they were formed, with the majority of the cone-in-cone structures being composed of calcite with thin layers of clay between cones. There are also, more rarely, structures composed of siderite, gypsum, pyrite. There are also some instances of cone-in-cone occurring within coals. Often the cone-in-cone will be found as features of calcite layers within a shale, and rarely within a dedolomite (calcitized dolomite).