Rugose corals are extinct solitary or colonial organisms known for their distinctive horn-shaped exoskeleton, often referred to as horn coral. They are commonly found in Paleozoic limestone deposits, where collectors prize them for their clear internal septal arrangements visible in cross-section. Specimens are typically preserved through calcite replacement, often forming robust fossils that are easy to clean and display.

Hardness

3-4

Mohs

Luster

Dull to Vitreous

Streak

White

Transparency

Opaque

fossilcommon

Rugose Coral

Also: Horn coral

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

Is this rugose 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 rugose coral with a known reference. Rugose 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. Rugose Coral leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Rugose Coral typically shows a dull to vitreous luster.
4
Match the color range
Compare against the expected color range: white, gray, brown, tan.
5
Look at form & habit
Typical habit: horn-shaped or solitary conical corallite.

Often found alongside rugose coral

Minerals reported to co-occur with rugose 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: 2.6-2.9 g/cm³
Colors: White Gray Brown Tan
Streak: White
Luster: Dull to Vitreous
Transparency: Opaque
Crystal habit: Horn-shaped or Solitary Conical Corallite
Cleavage: None
Rarity: Common
Uses: Collector, Decorative, Paleontological Study
Host rock: Limestone
Typical price: $5-50 per specimen

Where rockhounds find rugose coral

Classic worldwide localities

Indiana
Kentucky
Ohio
Gotland
Morocco

Field-hunting tip

Look in limestone country — that is the host setting where rugose 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 or solitary conical corallite habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify rugose coral?+

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

Where is rugose coral found?+

Notable localities include Indiana; Kentucky; Ohio; Gotland; Morocco.

How much is rugose coral worth?+

Typical asking prices fall in the range of $5-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What minerals are found with rugose coral?+

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

What kind of rock does rugose coral form in?+

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

What is rugose coral used for?+

Rugose Coral is used in collector, decorative, paleontological study.

Find rugose coral on the map

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