sedimentary (fossil)

Trilobite Pygidium (Tail Segment)

Phylum Arthropoda, Class Trilobita (likely order Phacopida)

Hardness: 3 (calcite replacement); Color: Grey, brown, or tan; Luster: Dull/earthy; Structure: Distinct segmented lobes consisting of an axial lobe and two pleural lobes; Composition: Fossilized remains often replaced by Calcium Carbonate (CaCO3).

Hardness: 3 (calcite replacement)
Color: Grey, brown, or tan
Luster: Dull/earthy

Identified March 7, 2026More sedimentary (fossil) →

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Physical properties

Formation & geological history

Formed through permineralization in marine sedimentary environments during the Paleozoic era (approx. 521 to 252 million years ago). They were ancient marine arthropods that inhabited the sea floor.

Uses & applications

Primarily used for academic study, stratigraphic correlation in geology, and as popular items for private fossil collections and educational displays.

Geological facts

Trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years. They are extinct relatives of modern horseshoe crabs and spiders. This specific piece is a 'pygidium,' which is the posterior (tail) section of the creature.

Field identification & locations

Identify in the field by looking for symmetrical rib-like segments in limestone or shale outcrops. Common in Ohio, Utah, Morocco, and Russia. For collectors: look for sharp detail in the segment ribs and lack of crushing.

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