Rocksday

Nummulite

Nummulite is a fossil with a Mohs hardness of about 3 and a dull luster, usually white, gray or yellow.

Coin-shaped shells of giant foraminifera, common in Eocene and Miocene limestones around the Mediterranean.

Nummulite specimen
Photo: Wilson44691, Public domain, via Wikimedia Commons

How to identify nummulite

  • Flat disks from about a centimeter to a few centimeters across.
  • A broken one shows a tight spiral of tiny chambers.
  • The limestone fizzes in acid.

Often confused with

Where it's found

  • Egypt
  • Mediterranean region
  • Pakistan

Uses

Dating Eocene rocks. The limestone itself is a building stone.

Rock tumbling

Not suitable for tumbling.

Did you know?

Egyptian pyramid limestone is full of them. Ancient writers compared the disks to petrified lentils.

Nummulite FAQ

What is nummulite?

Nummulite is a fossil with a Mohs hardness of about 3 and a dull luster, usually white, gray or yellow. Coin-shaped shells of giant foraminifera, common in Eocene and Miocene limestones around the Mediterranean.

How do you identify nummulite?

Flat disks from about a centimeter to a few centimeters across. A broken one shows a tight spiral of tiny chambers. The limestone fizzes in acid.

How hard is nummulite?

Nummulite has a Mohs hardness of about 3. A steel knife scratches Nummulite, but a fingernail doesn't.

Where is nummulite found?

Notable localities include Egypt, Mediterranean region and Pakistan.

What is nummulite used for?

Dating Eocene rocks. The limestone itself is a building stone.

Can you tumble nummulite?

It isn't a good choice for a rock tumbler.

What is nummulite often confused with?

Nummulite is most often confused with Fusulinid and Crinoid. Fusulinids are rice-grain shaped and are older, from the late Paleozoic. Crinoid stem pieces are small discs, often with a center hole, not a spiral coin.

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