sedimentary

Ammonite Fossil

Ammonoidea (subclass)

Hardness: 3-4 (if calcified/pyritized); Color: brown, tan, or metallic if pyritized; Luster: earthy to pearly; Crystal structure: orthorhombic/hexagonal (aragonite/calcite replacement); coiled chambered shell with ribbing.

Hardness: 3-4 (if calcified/pyritized)
Color: brown, tan, or metallic if pyritized
Luster: earthy to pearly

Identified April 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the process of permineralization or replacement where mud and minerals fill the shell of a prehistoric cephalopod. These specimens date from the Devonian to the Cretaceous period (approx. 400 to 66 million years ago).

Uses & applications

Used primarily for paleontological study, jewelry (especially iridescent 'Ammolite'), home decor, and educational collections.

Geological facts

Ammonites are extinct marine mollusks related to modern squids and octopuses. Their name comes from the Egyptian god Ammon, who was often depicted with ram's horns which the fossils resemble.

Field identification & locations

Identify by its spiral shape and distinctive ribbing. Commonly found in sedimentary rock formations like shale or limestone. Collectors look for sutures (growth lines) or opal-like iridescence on the surface.