Rocksday

Orthoceras

Straight, cone-shaped shells of ancient nautiloids, often polished in black limestone plates.

Orthoceras specimen
Photo: Parent Géry, CC BY-SA 3.0, via Wikimedia Commons

How to identify orthoceras

  • Long straight cones with chamber walls across them.
  • Often in polished black or red limestone.
  • Fizzes in acid.

Often confused with

Where it's found

  • Erfoud, Morocco
  • Öland, Sweden
  • Baltic region

Uses

Decorative plates and collecting.

Rock tumbling

Not suitable for tumbling.

Did you know?

Its name means 'straight horn'.

Think you could spot it from a blurry close-up?

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