sedimentary
Ammonite Fossil in Limestone Matrix
Ammonoidea (subclass) in Calcium Carbonate (CaCO3)
Hardness: 3-4 (matrix); Color: Tan, grey-brown; Luster: Dull/earthy; Structure: Spiral chambered shell casts; Cleavage: None (conchoidal fracture when broken)
- Hardness
- 3-4 (matrix)
- Color
- Tan, grey-brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 3-4 (matrix); Color: Tan, grey-brown; Luster: Dull/earthy; Structure: Spiral chambered shell casts; Cleavage: None (conchoidal fracture when broken)
Formation & geological history
Formed through the process of permineralization in a marine environment during the Jurassic to Cretaceous periods (approx. 200–66 million years ago). The sediment turned into rock over millions of years around the dead cephalopod.
Uses & applications
Primarily used as educational specimens, collectibles, and decorative items. In some cases, polished fossils are used in jewelry.
Geological facts
Ammonites are extinct marine mollusks related to the modern-day squid and octopus. They are 'index fossils,' used by geologists to date the layer of rock in which they are found.
Field identification & locations
Identify by the distinctive 'C' shaped or spiral 'ram's horn' patterns on the surface of the rock. Commonly found in coastal areas, riverbeds, and quarries that expose ancient seabed layers.
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