fossil

Fossil Coral

Hexagonaria or Rugose coral fossil (Calcium carbonate, CaCO3)

Hardness of 3-4 on the Mohs scale, tan to grey color, dull to vitreous luster, hexagonal or tubular skeletal structures.

Identified November 1, 2026More fossil →

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Physical properties

Hardness of 3-4 on the Mohs scale, tan to grey color, dull to vitreous luster, hexagonal or tubular skeletal structures.

Formed in warm, shallow ancient Paleozoic seas approximately 350-400 million years ago when coral skeletons were replaced by silica or calcite.

Used in lapidary arts, wire-wrapped jewelry, and as educational fossil specimens for collectors.

Many fossil corals are state stones, such as Petoskey stone from Michigan, and preserve ancient marine ecosystems.

Identify by characteristic star-like corallites or honeycomb patterns on weathered limestone surfaces globally.

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image