fossil

Fossilized Brachiopod

Brachiopoda (e.g., Atrypa or Rhynchonellida)

Hardness: 3-3.5 (calcite replacement) or 7 (silicified/quartz replacement); Color: grayish-tan, buff, to light brown; Luster: dull to earthy; Structure: bivalved shell shape with distinct radial ribs/costae and a curved hinge line.

Hardness: 3-3
Color: grayish-tan, buff, to light brown
Luster: dull to earthy

Identified July 22, 2026More fossil →

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Physical properties

Formation & geological history

Formed when marine invertebrates with two unequal shells died and were buried in marine sediments. Over millions of years (typically Paleozoic era, ~250-500 million years ago), the shell organic material was replaced by calcite, silica, or pyrite.

Uses & applications

Educational tools, geological indicators for biostratigraphy, fossil collections, and decorative displays.

Geological facts

Brachiopods are marine animals that look superficially like bivalve mollusks (clams), but they belong to a completely different phylum. Unlike clams which have left and right symmetric shells, brachiopods have top and bottom shells where each individual shell is bilaterally symmetrical.

Field identification & locations

Can be identified by the fan-like ribbed pattern radiating from the beak/hinge of the shell. Common in sedimentary rock layers like limestone and shale worldwide, especially in areas with ancient seafloor deposits.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

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Fossiliferous Limestone

Biogenic Limestone with Brachiopod/Crinoid fragments

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Horn Coral (Rugose Coral)

Order Rugosa (extinct)

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