sedimentary
Ammonite Fossil
Ammonoidea (Calcium carbonate or Pyrite replaced)
Hardness: 3.5-4 (Mohs scale), Color: Brown, tan, reddish-brown, Luster: Pearly to dull, Crystal Structure: Orthorhombic/Hexagonal (depends on mineralization), Cleavage: None, Specific Gravity: 2.6-2.9
- Hardness
- 3
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Physical properties
Hardness: 3.5-4 (Mohs scale), Color: Brown, tan, reddish-brown, Luster: Pearly to dull, Crystal Structure: Orthorhombic/Hexagonal (depends on mineralization), Cleavage: None, Specific Gravity: 2.6-2.9
Formation & geological history
Formed through permineralization of extinct marine mollusks in sedimentary environments. Most date from the Devonian period through the Cretaceous (approx. 400 to 66 million years ago). Found in shale, limestone, and sandstone layers.
Uses & applications
Used in decorative jewelry (often sliced to show internal chambers), home decor, as educational specimens for paleontology, and in lithotherapy/collecting.
Geological facts
Ammonites are more closely related to octopuses and squids than to the modern Nautilus they resemble. Some species can reach over 2 meters in diameter. They went extinct at the same time as the dinosaurs.
Field identification & locations
Identify by its spiral-coiled shell shape and 'suture patterns' (complex lines where internal walls meet the shell). Commonly found in Morocco, Madagascar, the UK (Lyme Regis), and Western USA. Collectors should look for symmetry and internal chamber clarity.
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