fossil

Fossil coral fragment

Fossilized colonial coral, commonly *Hexagonaria* (often called Petoskey stone) or related scleractinian/tabulate coral

AI-generated identification · may be incorrect

Pale cream to gray, porous and irregularly patterned, with small coral corallites; mainly recrystallized calcite/aragonite. Mohs hardness about 3–4, dull to waxy luster, and no prominent cleavage.

Identified August 16, 2026More fossil →

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At a glance

Common name: Fossil coral fragment
Scientific name: Fossilized colonial coral, commonly *Hexagonaria* (often called Petoskey stone) or related scleractinian/tabulate coral
Category: fossil
Identified: August 16, 2026
Method: Standard

AI Estimated Value

About $5–$25 for a common rough fragment; $20–$100 or more for large, well-preserved, polished, or locality-documented specimens.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Pale cream to gray, porous and irregularly patterned, with small coral corallites; mainly recrystallized calcite/aragonite. Mohs hardness about 3–4, dull to waxy luster, and no prominent cleavage.

Formation & geological history

A marine coral colony was buried and mineralized, commonly during the Paleozoic (roughly 250–450 million years ago); silica or calcite-rich groundwater preserved and replaced the original skeleton.

Uses & applications

Used as a geological collectible, teaching specimen, and ornamental stone; polished examples are made into cabochons and small carvings, but this rough piece has limited commercial use.

Geological facts

The honeycomb-like surface represents individual coral animals (corallites), not holes formed by modern erosion. Identification to species is uncertain without a polished cross-section and locality information.

Field identification & locations

Common fossil corals occur in Paleozoic marine limestone deposits, especially around the Great Lakes and other former shallow seas. Look for repeated corallite cups or polygonal honeycomb patterns and test cautiously with dilute acid, which may fizz if calcitic.