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 — that is 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.
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.
