Rock Identifier
Fossilized Bivalve Shell (Fossilized Clam) (Bivalvia (class) / CaCO3 (Calcium Carbonate)) — fossil
fossil

Fossilized Bivalve Shell (Fossilized Clam)

Bivalvia (class) / CaCO3 (Calcium Carbonate)

Hardness: 3-3.5 on Mohs scale (calcite replacement) or 6.5-7 (if silicified/agateized); Color: Off-white, cream, yellowish to tan; Luster: Pearly to dull, vitreous where agatized; Structure: Fan-shaped shell structure with concentric growth lines.

Hardness
3-3
Color
Off-white, cream, yellowish to tan
Luster
Pearly to dull, vitreous where agatized
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Physical properties

Hardness: 3-3.5 on Mohs scale (calcite replacement) or 6.5-7 (if silicified/agateized); Color: Off-white, cream, yellowish to tan; Luster: Pearly to dull, vitreous where agatized; Structure: Fan-shaped shell structure with concentric growth lines.

Formation & geological history

Formed through the burial of ancient marine bivalve mollusks in marine or freshwater sediments. Over millions of years, organic shells undergo permineralization or recrystallization, replacing original aragonite/calcite with stable calcite or silica.

Uses & applications

Used in educational collections, fossil displays, lapidary arts, and jewelry when silicified or opalized.

Geological facts

Bivalves have existed since the early Cambrian period over 500 million years ago. Distinct concentric growth rings on the shell reflect seasonal growth patterns, similar to tree rings.

Field identification & locations

Identified by its characteristic symmetrical paired shell shape with distinct concentric growth ridges. Commonly found in sedimentary rock formations, coastal beach deposits, and limestone quarries worldwide.

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