Fossilized coral in the United States.
- Sep 11, 2024
- 2 min read
For hundreds of millions of years, the oceans have been home to numerous marine species, among which fossilized coral plays a significant role. Although these marine creatures are primarily associated with aquatic environments, their fossils can sometimes be found thousands of kilometers away from their original habitat.
Photos : Emmanuel Thoreux.
Among the best-known coral fossils are those from Indonesia, famous for their cream and light brown colors. But there are also exceptional gemological curiosities, such as corals pseudomorphized into demantoid garnet—extremely rare specimens highly sought after by collectors (see the GIA article for more information: Demantoid Garnet Fossil Pseudomorphs).
Fossilized corals are also found throughout North America, in a variety of forms, colors, and species. This article highlights some iconic examples found on this continent, including fossils that are as beautiful as they are fascinating.
Petoskey Stone from Michigan: An Iconic Fossil
The Petoskey stone is one of Michigan’s most famous coral fossils, and it was even designated as the state stone in 1965. The name comes from the city of Petoskey, located in Emmet County. The origin of the name may stem from a legend of the Ottawa Indians and Chief Pet-O-Sega. The Petoskey stone is composed of fossilized coral colonies of the genus Hexagonaria percarinata, dating from the Middle Devonian period, approximately 350 million years ago. These fossils come from a stratum called the Gravel Point Formation and are found only in this specific formation, often dislodged from their host rock during periods of glaciation.
Photos : Emmanuel Thoreux
Photo : Emmanuel Thoreux
Fossilized coral from Alaska, genus Hexagonaria.
Fossilized coral of the genus Hexagonaria is also found in Alaska. These marine fossils come from geological formations similar to those found in Michigan, but they are concentrated in this northern region of the United States, offering a fascinating geological diversity.
Photos : Emmanuel Thoreux
Fossilized Horn Coral from Utah: An Exceptional Red Specimen.
The Horn coral fossil found in Utah is distinguished by its deep red color. These fossilized corals originate from Lophophyllidium coral reefs, which thrived during the Pennsylvanian period, approximately 300 million years ago. Today, the fossils are extracted from the Morgan Formation, around the Kamas area in Utah. Horn coral specimens can feature translucent structures and fascinating details that are highly prized by collectors and gem cutters.
Photos : Emmanuel Thoreux
Coral fossils are not only a natural wonder, but they also represent valuable geological curiosities for collectors and gem enthusiasts. Whether it’s the fossilized corals of Michigan, the Hexagonaria corals of Alaska, or the Horn corals of Utah, each fossil tells a fascinating story of the evolution of marine life across geological eras.
These rare and magnificent fossils are a precious testament to the past and the natural riches hidden beneath our feet. Exploring them provides a deeper understanding of Earth’s history and allows us to admire unique geological treasures that captivate both scientists and collectors alike.
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