Judging quality
Look for a repeating radial floret pattern rather than random banding, and for silicified hardness — genuine agatised coral will not scratch with a steel blade.
Fossil
Fossil Coral
Colonial coral replaced by agate or chalcedony, preserving the flower-like corallite pattern as a permanent stone. Florida agatised coral shows crisp white florets in grey; Petoskey stone from Michigan is a Devonian rugose coral polished to a honeycomb.
Care
Durable. Wash with water; Petoskey stone benefits from occasional light waxing to keep the pattern visible when dry.
History & lore
Petoskey stone is the state stone of Michigan and is named for the Odawa leader Chief Pet-O-Sega.
Cultural history, recorded as tradition rather than as medical or scientific claim.
Common questions about Fossil Coral
- What is Fossil Coral?
- Colonial coral replaced by agate or chalcedony, preserving the flower-like corallite pattern as a permanent stone. Florida agatised coral shows crisp white florets in grey; Petoskey stone from Michigan is a Devonian rugose coral polished to a honeycomb.
- How hard is Fossil Coral and what is it made of?
- Fossil Coral is a Fossil-family mineral with the composition SiO2 after CaCO3. It crystallizes in the trigonal system and rates 6.5-7 on the Mohs hardness scale. It occurs in tan, grey, cream, brown.
- Where does Fossil Coral come from?
- Notable localities for Fossil Coral include Florida, USA, Indonesia, Michigan (Petoskey stone).
- How do you tell good Fossil Coral from filler?
- Look for a repeating radial floret pattern rather than random banding, and for silicified hardness — genuine agatised coral will not scratch with a steel blade.
- How do you care for Fossil Coral?
- Durable. Wash with water; Petoskey stone benefits from occasional light waxing to keep the pattern visible when dry.
See it in person
Photographs only go so far
Both rooms are open six days a week, and there is always someone happy to pull pieces out of the case so you can compare them under the light.