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.

Hardness

3-4

Mohs

Luster

Dull to Waxy

Streak

White

Transparency

Opaque

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Horn Coral

Also: Rugosa, Rugose coral

Hardness: 3-4
Luster: Dull to Waxy
Streak: White
Transparency: Opaque

Is this horn coral?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try 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.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Horn Coral leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Horn Coral typically shows a dull to waxy luster.
4
Match the color range
Compare against the expected color range: gray, tan, brown, white.
5
Look at form & habit
Typical habit: horn-shaped, conical, solitary.

Often confused with

Horn Coral vs. its common look-alikes — and how to tell them apart in the field.

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Wood Opal

Mohs 5.5-6.5

How to tell apart: Wood Opal is the harder of the two (Mohs 5.5-6.5 vs. 3-4); luster reads dull to waxy on Horn Coral and vitreous on Wood Opal.

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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
Colors: Gray Tan Brown White
Streak: White
Luster: Dull to Waxy
Transparency: Opaque
Crystal habit: Horn-shaped, Conical, Solitary
Cleavage: None
Rarity: Common
Uses: Collector, Educational, Lapidary
Host rock: Limestone, Shale
Typical price: $2-20 per specimen

Where rockhounds find horn coral

Classic worldwide localities

USA (Midwest)
Canada (Ontario)
United Kingdom
Germany
Morocco

Field-hunting tip

Look in limestone, shale country — that is the host setting where horn coral typically forms. If you start seeing calcite, dolomite, quartz in float, you are in the right ground. Field specimens usually show a horn-shaped, conical, solitary habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify horn coral?+

Mohs hardness is 3-4. It typically shows a dull to waxy luster. The streak is white. Common colors include gray, tan, brown, white.

Where is horn coral found?+

Notable localities include USA (Midwest); Canada (Ontario); United Kingdom; Germany; Morocco.

How much is horn coral worth?+

Typical asking prices fall in the range of $2-20 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like horn coral?+

Horn Coral is most often confused with Wood Opal. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with horn coral?+

Horn Coral commonly co-occurs with Calcite, Dolomite, Quartz, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does horn coral form in?+

Horn Coral typically forms in limestone, shale. Working float back to the host body is the standard way to chase a fresh occurrence.

What is horn coral used for?+

Horn Coral is used in collector, educational, lapidary.

Find horn coral on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.