sedimentary
Ammonite Fossil
Ammonoidea (typically preserved as Calcite or Aragonite)
Hardness: 3.5-4 (Calcite composition); Color: Tan, cream, or brownish-grey; Luster: Dull to earthy; Structure: Spiral planispiral coiling with visible ribbing and septa (chamber walls).
- Hardness
- 3
- Color
- Tan, cream, or brownish-grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 3.5-4 (Calcite composition); Color: Tan, cream, or brownish-grey; Luster: Dull to earthy; Structure: Spiral planispiral coiling with visible ribbing and septa (chamber walls).
Formation & geological history
Formed via permineralization or cast/mold formation within marine sedimentary layers. These specimens date from the Devonian period through the Cretaceous (approx. 400 to 66 million years ago).
Uses & applications
Primarily used for educational scientific study, decorative display, and jewelry (especially when fossilized as ammolite or iridescent opalized forms).
Geological facts
Ammonites are extinct cephalopods related to the modern nautilus. They are considered 'index fossils' because specific species can pinpoint the exact age of the rock layer they are found in.
Field identification & locations
Identify by the characteristic coiled 'ram's horn' shape and suture patterns. Commonly found in limestone, shale, or siltstone coastal cliffs and quarries globally, especially in Morocco, Madagascar, and the UK.
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