sedimentary

Bivalve Fossil in Sedimentary Matrix

Fossiliferous Mudstone (Class: Bivalvia)

AI-generated identification · may be incorrect

Hardness: 3-5 (matrix varies); Color: Gray, brown, and white; Luster: Dull/earthy matrix with pearly fossil highlights; Crystal Structure: Amorphous/cryptocrystalline; Cleavage: None

Hardness: 3-5 (matrix varies)
Color: Gray, brown, and white
Luster: Dull/earthy matrix with pearly fossil highlights

Identified May 29, 2026More sedimentary →

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Physical properties

Hardness: 3-5 (matrix varies); Color: Gray, brown, and white; Luster: Dull/earthy matrix with pearly fossil highlights; Crystal Structure: Amorphous/cryptocrystalline; Cleavage: None

Formation & geological history

Formed through the lithification of marine or freshwater sediment where shells were buried. The organic shell material is often replaced by minerals like calcite or aragonite over millions of years.

Uses & applications

Scientific research, educational use, and paleontological collecting. Sometimes used as decorative architectural stone if the density of fossils is high (coquina).

Geological facts

The concentric growth lines visible on the shell surface can sometimes be used to estimate the age of the mollusk when it died, similar to tree rings.

Field identification & locations

Look for visible symmetry and growth rings in sedimentary rock layers, particularly shales or limestones. Common in areas that were formerly ancient sea beds.