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, 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.