Rock Identifier
Fossilized Coral (Rugosa or Tabulate Coral Fossil (Replacement by Silica/Calcite)) — fossil
fossil

Fossilized Coral

Rugosa or Tabulate Coral Fossil (Replacement by Silica/Calcite)

Hardness: 6.5 to 7 on the Mohs scale if silicified (quartz replacement), or 3 if calcified. Color: Tan, brown, white, or grey. Luster: Vitreous to dull. Structure: Microcrystalline quartz or crystalline calcite forming distinctive columnar or honeycomb corallite structures.

Hardness
6
Color
Tan, brown, white, or grey
Luster
Vitreous to dull
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Physical properties

Hardness: 6.5 to 7 on the Mohs scale if silicified (quartz replacement), or 3 if calcified. Color: Tan, brown, white, or grey. Luster: Vitreous to dull. Structure: Microcrystalline quartz or crystalline calcite forming distinctive columnar or honeycomb corallite structures.

Formation & geological history

Formed in ancient shallow marine environments where coral skeletons were buried rapidly in sediment and underwent petrifaction, typically through permineralization or replacement by silica or calcium carbonate over hundreds of millions of years.

Uses & applications

Used primarily as a lapidary material for cabochons, decorative carvings, educational specimens, and by fossil collectors.

Geological facts

Many fossil corals found inland were formed during the Paleozoic era when shallow seas covered vast continental interiors, such as the Midwestern United States.

Field identification & locations

Easily identified in the field by the distinctive star-like, tubular, or honeycomb patterns representing individual coral polyps (corallites). Frequently found in limestone formations or glacial gravel deposits.

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