fossil

Fossilized Coral (Petoskey Stone or Tabulate Coral)

Scleractinia or Tabulata (CaCO3 - Calcium Carbonate)

AI-generated identification · may be incorrect

Hardness: 3-4 on Mohs scale; Color: Off-white, grey, light tan, or yellowish-brown; Luster: Dull to earthy when raw, vitreous to silky when polished; Structure: Distinctive honeycomb-like or corallite pore pattern; Cleavage: None (fossilized matrix)

Hardness: 3-4 on Mohs scale
Color: Off-white, grey, light tan, or yellowish-brown
Luster: Dull to earthy when raw, vitreous to silky when polished

Identified July 26, 2026More fossil →

Explore Fossilized Coral (Petoskey Stone or Tabulate Coral) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the fossilization of ancient coral reefs. Over millions of years, the organic calcium carbonate skeletal structures of marine coral polyps were buried in sediment and replaced or recrystallized by calcite or silica.

Uses & applications

Used widely for lapidary work, jewelry making, decorative stone carving, landscaping, and paleontology/geology educational collecting.

Geological facts

Fossil corals can range from Paleozoic species (over 400 million years old, such as favosites or chain corals) to modern Pleistocene reef fossils. A well-known variety in Michigan is the Petoskey Stone, which is a fossilized rugose coral.

Field identification & locations

Identified in the field by its distinctive repeating hexagonal or cellular structure resemble a honeycomb. Commonly found on beaches along ancient sea beds, lake shorelines (e.g., Lake Michigan), and limestone quarries. Collectors often test it with a drop of weak acid, which reacts with the calcium carbonate.