fossil

Fossilized Shell Fragment / Mother of Pearl

Calcium Carbonate (CaCO3) - Aragonite/Calcite biomineral

Hardness: 3.5-4.0 on Mohs scale. Color: Pearlescent white, off-white, with dark linear mineral markings. Luster: Pearly to nacreous on the inner surface. Structure: Fibrous/lamellar biomineral structure. Cleavage: Poor, splintery or conchoidal fracture.

Hardness: 3
Luster: Pearly to nacreous on the inner surface

Identified July 26, 2026More fossil →

Explore Fossilized Shell Fragment / Mother of Pearl in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed biogenically as the inner nacreous layer of a marine mollusk or bivalve shell. Over time, the organic components decay or fossilize while the aragonite/calcite structure remains preserved.

Uses & applications

Used primarily in decorative crafts, jewelry, inlay work, and collected as marine fossil or beachcombing specimens.

Geological facts

Nacre, or mother-of-pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer. Its iridescent pearly sheen is caused by the interference of light reflecting off alternating layers of aragonite platelets and organic biopolymers.

Field identification & locations

Can be identified in the field by its distinctive curved form, fibrous growth lines, and pearlescent, nacreous sheen on the concave side. Commonly found along coastal beaches and marine fossil beds.

Other fossil specimens

See all

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil

Fossiliferous Limestone

Limestone with embedded fossil cross-section

sedimentary

Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

sedimentary