Horn corals are extinct solitary corals characterized by their distinct horn-shaped, conical skeletons. They are commonly found in Paleozoic marine sedimentary rocks and are often preserved as calcite or silica replacements.
Is this horn 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 horn coral with a known reference. Horn Coral sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Rugose corals (class Rugosa). Age: Middle Ordovician to Late Permian.
- 3Check the preservationPreservation: Calcite skeleton. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: dull to waxy.
- 5Match the color rangeCompare against the expected color range: gray, tan, brown, white.
Often confused with
Horn Coral vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside horn coral
Minerals reported to co-occur with horn coral. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-4
- Density
- 2.7 g/cm³
- Luster
- Dull to waxy
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Collector, Educational, Lapidary
- Host rock
- Limestone, shale
- Organism
- Rugose corals (class Rugosa)
- Age
- Middle Ordovician to Late Permian
- Preservation
- Calcite skeleton
Where rockhounds find horn coral
22 mapped spotsClassic worldwide localities
- USA (Midwest)
- Canada (Ontario)
- United Kingdom
- Germany
- Morocco
U.S. states with horn coral
Each link opens a state-specific list of mapped rockhounding spots that produce horn coral.
Field-hunting tip
Where it forms: Limestone, shale. If you start seeing calcite, dolomite, quartz in float, you are in the right ground. In the U.S., the densest reported localities are in Michigan, Ohio, New York. Start trip planning there.
More horn coral photos
Common questions
How do you identify horn coral?+
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Find horn coral on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
