Rock Identifier
Coral fossil (likely fossilized colonial coral) (Calcareous fossil coral; commonly *Scleractinia* or *Tabulate/ rugose coral* (identification requires close pore-pattern examination)) — fossil
fossil

Coral fossil (likely fossilized colonial coral)

Calcareous fossil coral; commonly *Scleractinia* or *Tabulate/ rugose coral* (identification requires close pore-pattern examination)

AI-generated identification · may be incorrect

Cream to tan, dull-to-earthy luster, irregular branching and layered structure; composed mainly of microcrystalline calcite or aragonite. Mohs hardness is typically 3–4, with weak cleavage and specific gravity around 2.6–2.8; dilute acid may fizz.

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Physical properties

Cream to tan, dull-to-earthy luster, irregular branching and layered structure; composed mainly of microcrystalline calcite or aragonite. Mohs hardness is typically 3–4, with weak cleavage and specific gravity around 2.6–2.8; dilute acid may fizz.

Formation & geological history

Formed when a colonial coral skeleton accumulated calcium carbonate in a warm, shallow marine reef, then was buried and mineralized during diagenesis. Exact geological age is indeterminate from the image, ranging from Paleozoic to Cenozoic depending on coral type and locality.

Uses & applications

Primarily a fossil-collecting and educational specimen; stable pieces may be used decoratively, though cutting or trade can be restricted for protected fossil coral or modern coral.

Geological facts

The branching, repeated corallite structures are skeletal remains rather than crystal growth. A hand lens should reveal tiny polygonal or tubular chambers across broken surfaces.

Field identification & locations

Common fossil corals occur in ancient limestone and reef deposits worldwide, including the United States, Morocco, Madagascar, and Australia. Look for regular corallite pores and test a hidden spot with dilute hydrochloric acid; avoid confusing it with porous limestone or modern coral.

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Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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Weathered fossil bone fragment (identification uncertain)

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