Rock Identifier
Agatized Coral (Petrified Coral) (Agatized Fossil Coral (Silicon Dioxide, SiO2 replacement after Anthozoa)) — fossil
fossil

Agatized Coral (Petrified Coral)

Agatized Fossil Coral (Silicon Dioxide, SiO2 replacement after Anthozoa)

Hardness: 6.5-7 on Mohs scale; Color: yellowish-orange, brownish, tan, and translucent chalcedony grey; Luster: waxy to vitreous; Structure: cryptocrystalline quartz replacing honeycomb/corallite structures; Cleavage: none; Specific Gravity: ~2.6-2.65.

Hardness
6
Luster
waxy to vitreous
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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: yellowish-orange, brownish, tan, and translucent chalcedony grey; Luster: waxy to vitreous; Structure: cryptocrystalline quartz replacing honeycomb/corallite structures; Cleavage: none; Specific Gravity: ~2.6-2.65.

Formation & geological history

Formed through permineralization where silica-rich groundwater gradually replaced the calcium carbonate skeleton of ancient prehistoric coral reefs (often Oligocene-Miocene in age, around 20-30 million years old).

Uses & applications

Popular among rock collectors, lapidary artists, and jewelers; frequently cut into cabochons, slabbing specimens, or polished display pieces.

Geological facts

Agatized coral is the official state stone of Florida. It forms when ancient ocean floor corals are buried under sediment and fossilized by silica-rich water through microcrystalline quartz deposition.

Field identification & locations

Identified by the distinct flower-like or honeycomb pattern of individual corallites visible in cross-section with translucent chalcedony/agate infilling. Commonly found in Florida, Georgia, and Indonesia.

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