mineral

Chalcedony (Agatized Coral / Rough Chalcedony Node)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Tan, cream, white, with translucent patches. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (Trigonal). Cleavage: None (Conchoidal fracture). Specific Gravity: 2.6-2.64.

Hardness: 6
Color: Tan, cream, white, with translucent patches
Luster: Waxy to dull

Identified April 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich groundwater filling cavities in limestone or replacing organic material (like coral) over millions of years; often associated with Tertiary period formations.

Uses & applications

Lapidary work (cabs and tumbling), jewelry making, aquarium decor, and popular as a collector's specimen.

Geological facts

This specimen appears to be anagatized coral or a similar botryoidal chalcedony node. Over time, the original calcium carbonate of the coral skeleton was replaced by silica. Some pieces contain beautiful geodes or 'druzy' quartz inside the vugs.

Field identification & locations

Identify by its 'waxy' texture when broken, high hardness (cannot be scratched by a steel knife), and translucent edges when held to a light source. Commonly found in Florida, Georgia, and riverbeds in the Southeast US.

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