sedimentary

Ammonite Fossil

Ammonoidea (primarily composed of Calcite, CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite replacement); Color: Yellow, brown, tan, or white; Luster: Vitreous to pearly; Structure: Spiral planispiral chambers; Cleavage: None (fossilized structure)

Hardness: 3-4 (Calcite replacement)
Color: Yellow, brown, tan, or white
Luster: Vitreous to pearly

Identified March 2, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Calcite replacement); Color: Yellow, brown, tan, or white; Luster: Vitreous to pearly; Structure: Spiral planispiral chambers; Cleavage: None (fossilized structure)

Formation & geological history

Formed through permineralization of extinct marine cephalopods in marine sedimentary environments during the Devonian to Cretaceous periods (approx. 400 to 66 million years ago).

Uses & applications

Used primarily as decorative collector specimens, educational material, and in jewelry (pendants and cabochons).

Geological facts

Ammonites are more closely related to living squid and octopuses than to the nautilus they resemble. Large specimens can grow up to several feet in diameter.

Field identification & locations

Identified by the distinct coiled shell divided into septa (internal walls). Commonly found in sedimentary outcrops, particularly in Madagascar, Morocco, and the UK. Look for the suture patterns on the exterior.