sedimentary

Spondylus Oyster Calcification / Fossilized Oyster

Spondylus (Thorny Oyster) / Calcium Carbonate (CaCO3)

Hardness: 3.0 (calcareous); Color: Grayish-tan, iridescent, often with green algae staining; Luster: Pearly to dull; Structure: Irregular bivalve growth; Shell is composed of calcite and aragonite layers.

Hardness: 3
Color: Grayish-tan, iridescent, often with green algae staining
Luster: Pearly to dull

Identified April 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Biogenic sedimentary formation. These specimens are formed by the accumulation and mineralization of calcium carbonate shells from marine mollusks, often found in coastal deposits or marine limestone layers ranging from Eocene to Holocene periods.

Uses & applications

Primarily for shell collecting, marine biology study, and occasionally used in traditional jewelry or 'heishe' beads in certain cultures (like the Ancestral Puebloans).

Geological facts

Spondylus shells were once used as a form of currency and prestige objects in pre-Columbia South America. They are often called 'thorny oysters' despite not being true oysters.

Field identification & locations

Identify by looking for the irregular, spiked (thorny) growth patterns and the remaining pearly luster on the interior. Commonly found on beaches or in uplifted marine sediment beds.

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