sedimentary

Ammonite Fossil

Ammonoidea (Calcium carbonate - CaCO3)

AI-generated identification · may be incorrect

Hardness: 3.5-4 (Mohs scale), Color: Brown, tan, cream with white suture lines, Luster: Vitreous to pearly when polished, Structure: Planispiral coiled shell with complex suture patterns, Specific Gravity: 2.7

Hardness: 3

Identified March 31, 2026More sedimentary →

Explore Ammonite Fossil 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 permineralization where minerals like calcite or aragonite replace organic matter over millions of years. These specimens primarily date from the Devonian to the Cretaceous period (approx. 400 to 66 million years ago).

Uses & applications

Used widely in decorative arts, jewelry (cabochons), as high-end home decor, and educational/museum specimens for paleontological study.

Geological facts

Ammonites are extinct cephalopods related to the modern nautilus; their name is derived from the Egyptian god Ammon, who was depicted with rams' horns. They are excellent index fossils because they evolved rapidly and are found globally.

Field identification & locations

Identify by the characteristic coiled shape and 'leaf-like' or 'zigzag' suture lines (septa) showing through the shell. Common in marine-deposit sedimentary regions like Madagascar, Morocco, and the UK.