sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
Hardness: 3 (Calcite-based), Color: Tan to brownish-gray, Luster: Dull to earthy, Crystal structure: Trigonal (microcrystalline calcite), Features: Nesting concentric cones with ribbed or grooved surfaces.
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Physical properties
Hardness: 3 (Calcite-based), Color: Tan to brownish-gray, Luster: Dull to earthy, Crystal structure: Trigonal (microcrystalline calcite), Features: Nesting concentric cones with ribbed or grooved surfaces.
Formation & geological history
Formed via diagenetic processes during the compaction and dewatering of carbonate-rich sediments, likely during the Paleozoic or Mesozoic eras. The cones develop through pressure solution and mineral growth between layers.
Uses & applications
Primarily of interest to geological collectors, researchers, and for educational study of sedimentary structures.
Geological facts
These structures are often mistaken for fossils like teeth or wood because of their unusual geometric shape, but they are entirely inorganic sedimentary features.
Field identification & locations
Identify by the unique 'nesting doll' cone appearance and vertical ribbing. Commonly found in shale beds or associated with large limestone concretions in areas like the American Midwest or the UK.
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