Rock Identifier
Brachiopod Fossil (Brachiopoda (Phylum); often Atrypa or Mucrospirifer genus depending on locality) — fossil
fossil

Brachiopod Fossil

Brachiopoda (Phylum); often Atrypa or Mucrospirifer genus depending on locality

Hardness: 3-4 (Calcite composition). Color: Tan, beige, or gray. Luster: Dull to earthy. Structure: Bilateral symmetry across the valves. Features distinct radiating ribs or costae.

Hardness
3-4 (Calcite composition)
Color
Tan, beige, or gray
Luster
Dull to earthy
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Physical properties

Hardness: 3-4 (Calcite composition). Color: Tan, beige, or gray. Luster: Dull to earthy. Structure: Bilateral symmetry across the valves. Features distinct radiating ribs or costae.

Formation & geological history

Formed through permineralization of marine organisms in sedimentary environments. Most common specimens date from the Paleozoic Era (approx. 541 to 252 million years ago).

Uses & applications

Used primarily for scientific study, as index fossils for dating rock layers, and for educational or private collections.

Geological facts

Although they look like clams, brachiopods are not mollusks. They belong to a distinct phylum and have a unique feeding organ called a lophophore. They were once the most dominant life form on the ocean floor.

Field identification & locations

Identify in the field by looking for the 'lampshell' shape in limestone or shale outcrops. Common in areas with exposed Paleozoic marine sediments like the US Midwest or the UK.

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