Orthoceras is an extinct genus of nautiloid cephalopod characterized by its distinctive straight, conical shell. These fossils are frequently found embedded in limestone matrices and are popular in lapidary for their aesthetic internal chamber patterns, which often show white calcite crystallization.

Hardness

3-4

Mohs

Luster

Dull to Vitreous

Streak

White

Transparency

Opaque

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Orthoceras

Also: Orthoceratite

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

Is this orthoceras?

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 orthoceras with a known reference. Orthoceras 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. Orthoceras leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Orthoceras typically shows a dull to vitreous luster.
4
Match the color range
Compare against the expected color range: black, brown, gray, white.
5
Look at form & habit
Typical habit: straight, conical shell.

Often found alongside orthoceras

Minerals reported to co-occur with orthoceras. 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: Black Brown Gray White
Streak: White
Luster: Dull to Vitreous
Transparency: Opaque
Crystal habit: Straight, Conical Shell
Cleavage: None
Rarity: Common
Uses: Collector, Decorative, Lapidary
Host rock: Limestone
Typical price: $5-50 depending on size and polish

Where rockhounds find orthoceras

Classic worldwide localities

Morocco
Sweden
Estonia
United States

Field-hunting tip

Look in limestone country — that is the host setting where orthoceras typically forms. If you start seeing calcite, limestone in float, you are in the right ground. Field specimens usually show a straight, conical shell habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify orthoceras?+

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

Where is orthoceras found?+

Notable localities include Morocco; Sweden; Estonia; United States.

How much is orthoceras worth?+

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

What minerals are found with orthoceras?+

Orthoceras commonly co-occurs with Calcite, Limestone. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does orthoceras form in?+

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

What is orthoceras used for?+

Orthoceras is used in collector, decorative, lapidary.

Find orthoceras on the map

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