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.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Petrified Coral leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Petrified Coral typically shows a waxy to vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, brown, red, pink, yellow.
- 5Look at form & habitTypical habit: pseudomorphous after coral.
Often confused with
Petrified Coral vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads waxy to vitreous on Petrified Coral and waxy on Agate.
How to tell apart: Luster reads waxy to vitreous on Petrified Coral and waxy on Chalcedony.
How to tell apart: Luster reads waxy to vitreous on Petrified Coral and vitreous on Wood Opal.
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
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Waxy to Vitreous
- Transparency
- Translucent
- Crystal habit
- Pseudomorphous After Coral
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Decorative, Collector
- Host rock
- Sedimentary Strata
- Typical price
- $5-50 for small specimens, $100+ for large polished displays
Where rockhounds find petrified coral
2 mapped spotsClassic worldwide localities
- Florida, USA
- Georgia, USA
- Indonesia
- Thailand
Field-hunting tip
Look in sedimentary strata country, the host setting where petrified coral typically forms. If you start seeing quartz, calcite, goethite in float, you are in the right ground. Field specimens usually show a pseudomorphous after coral habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Iowa. Start trip planning there.
More petrified coral photos
Common questions
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Find petrified coral on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
