fossil

Sea Shell Fragment (Calcium Carbonate)

Aragonite / Calcite (CaCO3)

Hardness: 3-3.5 on Mohs scale. Color: White to off-white with brownish streaks. Luster: Pearly to dull. Structure: Orthorhombic or Trigonal crystal structure within marine shell biomineralization. Cleavage: Poor.

Hardness: 3-3
Color: White to off-white with brownish streaks
Luster: Pearly to dull

Identified July 26, 2026More fossil →

Explore Sea Shell Fragment (Calcium Carbonate) 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 through biomineralization by marine mollusks (such as gastropods or bivalves) which extract calcium carbonate from ocean water to build protective shells. Fragmented and rounded by ocean wave action along shorelines.

Uses & applications

Used in beach crafts, jewelry, aggregate production, agricultural lime (when ground), and popular among beachcombers for collection.

Geological facts

Mollusk shells are composed primarily of aragonite or calcite, two polymorphs of calcium carbonate. Over geological time, buried shell beds compress to form biogenic limestone.

Field identification & locations

Identified by its smooth, curved, polished surface caused by water erosion, distinct spiral or hinge features, and reactivity with dilute acid (effervesces). Commonly found along ocean beaches and tidal zones.

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