sedimentary

Fossilized Brachiopod

Brachiopoda (Class Rhynchonellata or Spiriferida)

Hardness: 3-4 (calcitic). Color: Tan, brown, or grey. Luster: Dull to earthy. Structure: Bilateral symmetry across the valve, often with visible growth lines or ribs. Composition: Replaced by calcite or silica.

Hardness: 3-4 (calcitic)
Color: Tan, brown, or grey
Luster: Dull to earthy

Identified May 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the process of permineralization or recrystallization within marine sedimentary layers. These specimens typically date from the Paleozoic era (541 to 252 million years ago) and were marine bottom dwellers.

Uses & applications

Primarily used for educational purposes, scientific study (stratigraphy), and amateur fossil collecting. Small specimens are sometimes used in craft jewelry.

Geological facts

Brachiopods are often mistaken for clams, but unlike clams, their valves are different sizes and they possess a unique feeding organ called a lophophore. They survived the 'Great Dying' mass extinction, though their diversity was drastically reduced.

Field identification & locations

Identified by the distinct hinge line and symmetrical shell valves (pedicle and brachial). Frequently found in limestone, shale, or mudstone outcrops in the Midwestern United States and the UK.

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary