sedimentary

Cone-in-cone structure

Hardness: 3 (if calcite-rich). Color: Light brown, tan, to gray. Luster: Dull to earthy. Structure: Nested concentric cones with ribbed or grooved surfaces (longitudinal striae). Specific gravity: 2.7. Cleavage: Rhombohedral (microscopic).

Hardness: 3 (if calcite-rich)
Color: Light brown, tan, to gray
Luster: Dull to earthy

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Diagenetic origin formed through the compaction of plastic sediment and pressure solution, often occurring within calcareous shale or marl. Most are found in Paleozoic or Mesozoic strata.

Uses & applications

Primarily a geological curiosity and educational specimen. Occasionally used in ornamental landscaping or as a niche collector's item in lapidary work.

Geological facts

These structures are often mistaken for fossils like petrified wood or corals, but they are purely mechanical physical features. They are most famous for appearing in the Ohio Shale or the Pierre Shale of the United States.

Field identification & locations

Identify by looking for 'wood-like' fibers that are actually nested cones that fit inside one another. Commonly found in carbonate concretions within shale beds across the Midwest United States, UK, and Europe.