fossil
Fossil Coral (Silicified)
Anthozoa (Silicified Scleractinia or Tabulata)
Hardness: 6.5-7 (if silicified); Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Hexagonal or radiating pore structures (corallites); Cleavage: None
- Hardness
- 6
- Color
- Gray, tan, white, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (if silicified); Color: Gray, tan, white, brown; Luster: Waxy to dull; Structure: Hexagonal or radiating pore structures (corallites); Cleavage: None
Formation & geological history
Formed through permineralization where silica replaces the calcium carbonate structure of ancient coral colonies, typically in marine sedimentary environments during the Paleozoic to Mesozoic eras.
Uses & applications
Used for jewelry (petoskey stones/agate coral), lapidary art, aquarium decor, and educational/collector specimens.
Geological facts
Florida and Michigan are famous for silicified/petrified corals; Florida has even designated Agatized Coral as its state stone. These fossils represent ancient reef systems that existed millions of years ago.
Field identification & locations
Look for distinctive, repetitive patterns of small circles or star-shaped pits on the surface of rocks in limestone-rich areas or coastal regions. It is much harder than limestone and will not react to acid if fully silicified.
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