fossil

Polished fossil ammonite cross-section

Ammonoidea (extinct cephalopod; commonly Jurassic/Cretaceous ammonite)

AI-generated identification · may be incorrect

Fossilized chambered shell in tan-brown calcite, with visible coiled septa and sutures; hardness about 3–4, vitreous to waxy luster, irregular fracture, and calcite crystal structure. The polished surface and rim appear human-cut or finished.

Identified September 13, 2026More fossil →

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Physical properties

Formation & geological history

Ammonites were marine cephalopods whose aragonitic shells were buried in sediment and later mineralized, commonly during the Jurassic–Cretaceous (about 201–66 million years ago).

Uses & applications

Used as a decorative fossil, educational specimen, paperweight, and jewelry or cabochon material; value depends on size, preservation, sutures, and polish.

Geological facts

The spiral chambers housed a living animal in the outermost chamber; internal septa strengthened the shell and controlled buoyancy. Brown coloration commonly reflects iron-bearing mineralization.

Field identification & locations

Identify by the planispiral coil, repeated chambers, and radiating or intricately curved sutures; common sources include Morocco, Madagascar, England, Germany, and Canada. Avoid strong acids, which etch calcite.