Rock Identifier
Fossil Coral (Scleractinia (Fossilized Coral) / Calcium Carbonate (CaCO3) or Silica (SiO2)) — fossil
fossil

Fossil Coral

Scleractinia (Fossilized Coral) / Calcium Carbonate (CaCO3) or Silica (SiO2)

Hardness: 3-4 (if calcite) or 6.5-7 (if silicified/agateized). Color: Off-white, tan, beige, brownish grey. Luster: Dull, earthy to waxy/vitreous. Structure: Distinctive honeycomb, star, or cellular pore patterns created by ancient coral corallites.

Hardness
3-4 (if calcite) or 6
Color
Off-white, tan, beige, brownish grey
Luster
Dull, earthy to waxy/vitreous
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Physical properties

Hardness: 3-4 (if calcite) or 6.5-7 (if silicified/agateized). Color: Off-white, tan, beige, brownish grey. Luster: Dull, earthy to waxy/vitreous. Structure: Distinctive honeycomb, star, or cellular pore patterns created by ancient coral corallites.

Formation & geological history

Formed from marine organisms (corals) that secreted calcium carbonate exoskeletons. Over millions of years, these structures were buried in marine sediment, where mineral replacement (calcite or silica) fossilized the organic structures into rock.

Uses & applications

Used primarily in lapidary work, jewelry making (cabochons), aquarium decoration, landscaping, and paleontology collections.

Geological facts

Fossilized corals can range in age from Ordovician (over 450 million years old) to Pleistocene. In some regions like Florida and Michigan (Petoskey stones), fossil coral is designated as the official state stone or fossil.

Field identification & locations

Identified field-side by the repeating, webbed, or star-like pore structures (corallites) across the surface. Frequently found along marine shorelines, riverbeds, and ancient limestone sea deposits globally.

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