Petrified coral forms when ancient coral skeletons are replaced by silica through mineral-rich groundwater over millions of years. It is highly prized by lapidary artists for the intricate, flower-like patterns of the original polyp structures which become preserved in agate or chalcedony. Look for distinct radiating or honeycomb cellular patterns on polished surfaces.
Is this petrified coral?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch petrified coral with a known reference. Petrified Coral sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Corals (class Anthozoa).
- 3Check the preservationPreservation: Petrified by silica replacement. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: waxy to vitreous.
- 5Match the color rangeCompare against the expected color range: white, gray, brown, red, pink, yellow.
Often confused with
Petrified Coral vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside petrified coral
Minerals reported to co-occur with petrified coral. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Luster
- Waxy to vitreous
- Transparency
- Translucent
- Rarity
- Common
- Uses
- Lapidary, Decorative, Collector
- Host rock
- sedimentary strata
- Organism
- Corals (class Anthozoa)
- Preservation
- Petrified by silica replacement
Where rockhounds find petrified coral
2 mapped spotsClassic worldwide localities
- Florida, USA
- Georgia, USA
- Indonesia
- Thailand
Field-hunting tip
Where it forms: sedimentary strata. If you start seeing quartz, calcite, goethite in float, you are in the right ground. In the U.S., the densest reported localities are in Iowa. Start trip planning there.
More petrified coral photos
Common questions
How do you identify petrified coral?+
Where is petrified coral found?+
Can I find petrified coral in the United States?+
What rocks look like petrified coral?+
What minerals are found with petrified coral?+
What kind of rock does petrified coral form in?+
What is petrified coral used for?+
Find petrified coral on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
