Rock Identifier
Fossilized Coral in Chert (Anthozoa (Class) fossil in Cryptocrystalline Quartz (SiO2)) — fossil
fossil

Fossilized Coral in Chert

Anthozoa (Class) fossil in Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: White to tan with brown fossil markings. Luster: Dull to waxy. Structure: Fine-grained matrix with visible biological imprints. Cleavage: None (conchoidal fracture).

Hardness
6
Color
White to tan with brown fossil markings
Luster
Dull to waxy
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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: White to tan with brown fossil markings. Luster: Dull to waxy. Structure: Fine-grained matrix with visible biological imprints. Cleavage: None (conchoidal fracture).

Formation & geological history

Formed during the Devonian to Mississippian periods (approx. 300-400 million years ago). Siliceous fluids replaced organic coral structures in a shallow marine environment, later smoothed by water erosion.

Uses & applications

Primarily for fossil collecting, decorative stones, and educational specimens. Occasionally used in lapidary work for cabochons.

Geological facts

The small star-like or ribbed patterns on the surface are 'corallites,' the skeletal remains where individual coral polyps once lived. Often found as rounded river pebbles or 'Petoskey-style' stones.

Field identification & locations

Identified by the distinct geometric biological patterns embedded in a hard, smooth stone. Common in the Great Lakes region and limestone-rich riverbeds. Hardness helps distinguish it from softer limestone fossils.

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