Rock Identifier
Petrified Coral (Agatized Coral) (Fossilized Anthozoa (Silicon Dioxide replacement - SiO2)) — fossil
fossil

Petrified Coral (Agatized Coral)

Fossilized Anthozoa (Silicon Dioxide replacement - SiO2)

Hardness: 6.5 to 7 on the Mohs scale. Color: Brownish-grey, tan, whitish-pink, and pale beige. Luster: Waxy to vitreous. Structure: Microcrystalline chalcedony replacing original calcium carbonate septa structure. Specific gravity: ~2.6.

Hardness
6
Color
Brownish-grey, tan, whitish-pink, and pale beige
Luster
Waxy to vitreous
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Physical properties

Hardness: 6.5 to 7 on the Mohs scale. Color: Brownish-grey, tan, whitish-pink, and pale beige. Luster: Waxy to vitreous. Structure: Microcrystalline chalcedony replacing original calcium carbonate septa structure. Specific gravity: ~2.6.

Formation & geological history

Formed when ancient coral reefs (often Oligocene to Miocene in age, ~20-30 million years old) were buried in sediment. Silica-rich groundwater gradually replaced the original calcium carbonate skeletal structure with chalcedony/agate while preserving the original organic coral patterns.

Uses & applications

Used in jewelry making, lapidary arts, cabochons, decorative carvings, and collected as fossil/mineral specimens.

Geological facts

Agatized coral is the official Florida State Stone. Unlike most living corals which are protected, petrified coral is a fossilized rock that can be legally collected and processed.

Field identification & locations

Identified by the distinct flower-like or star-like patterns on smoothed or cross-sectioned surfaces, combined with quartz-family hardness. Commonly found in Florida, Indonesia, and various ancient ocean basin deposits worldwide.

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