sedimentary

Ammonite Fossil (Small Pyritized or Calcitized Internal Mold)

Ammonoidea

AI-generated identification · may be incorrect

Hardness: 3.5-4.0 (for calcite variety); Color: Pale grey to off-white; Luster: Dull/Earthy; Crystal Structure: Amorphous fossil structure; Cleavage: None; Specific Gravity: 2.6-2.9

Hardness: 3
Color: Pale grey to off-white
Luster: Dull/Earthy

Identified June 15, 2026More sedimentary →

Explore Ammonite Fossil (Small Pyritized or Calcitized Internal Mold) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3.5-4.0 (for calcite variety); Color: Pale grey to off-white; Luster: Dull/Earthy; Crystal Structure: Amorphous fossil structure; Cleavage: None; Specific Gravity: 2.6-2.9

Formation & geological history

Formed during the Devonian to Cretaceous periods (approx. 400-66 million years ago). These are the fossilized remains of extinct marine mollusks, formed when the shell was buried in sediment and minerals replaced the organic material.

Uses & applications

Primarily used for educational collections, jewelry (as pendants), and as decorative ornaments or geological study specimens.

Geological facts

Ammonites are more closely related to living coleoids (squids and octopuses) than they are to the pearly nautilus which they resemble. They are excellent index fossils, used by scientists to date the age of rock layers.

Field identification & locations

Identified by the distinct spiral 'phi' ratio shape and visible suture lines where the internal chambers (septa) met the outer shell. Common in sedimentary limestone or shale beds worldwide.