Rock Identifier
Polished fossil coral agate (Silicified coral (chalcedony, SiO₂)) — fossil
fossil

Polished fossil coral agate

Silicified coral (chalcedony, SiO₂)

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; polished, waxy-to-vitreous luster and mottled cream, brown, red, and gray colors. The silica is microcrystalline, with coral-like cellular patterns visible in the specimen.

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Physical properties

Hardness about 6.5–7 Mohs; polished, waxy-to-vitreous luster and mottled cream, brown, red, and gray colors. The silica is microcrystalline, with coral-like cellular patterns visible in the specimen.

Formation & geological history

Formed when silica replaced or filled a coral skeleton during fossilization, commonly in sedimentary deposits; the original coral may be hundreds of millions of years old, though its exact age cannot be determined from the photo.

Uses & applications

Cut and polished for cabochons, jewelry, ornaments, and collecting; not generally used as construction stone.

Geological facts

Silicified coral preserves the structure of ancient reefs while replacing the original skeletal material with chalcedony.

Field identification & locations

Look for repeating corallite cells or honeycomb-like patterns within the polished surface; common sources include Indonesia, Mexico, and the United States. Similar-looking patterned jasper can be difficult to distinguish without close inspection.

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