sedimentary

Ammonite Fossil

Ammonoidea (primarily composed of Calcite, CaCO3, or Pyrite)

AI-generated identification · may be incorrect

Hardness: 3.5-4 (Mohs scale); Color: Gray, brown, or earthy tones (sometimes iridescent); Luster: Dull to sub-metallic; Structure: Planispiral coiled shell with visible suture lines; Specific Gravity: 2.7

Hardness: 3
Color: Gray, brown, or earthy tones (sometimes iridescent)
Luster: Dull to sub-metallic

Identified March 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the process of permineralization or replacement within marine sedimentary environments (shale, limestone, or mudstone). These cephalopods lived from the Devonian period through the Cretaceous (approx. 400 to 66 million years ago).

Uses & applications

Primary use in educational collections, fossil hunting, and jewelry (especially when opalized). Large, well-preserved slabs are used as decorative architectural elements or high-end interior design focal points.

Geological facts

Ammonites are extinct marine mollusks closely related to modern chambered nautiluses and squids. Their name is derived from the Egyptian god Ammon, who was depicted wearing ram's horns, which look similar to the fossil's coiled shape.

Field identification & locations

Identify by looking for the distinct 'sidebar' or 'ram's horn' spiral. In the field, look for ribbing patterns and suture lines where internal walls met the outer shell. Commonly found in coastal cliffs or limestone quarries where ancient seas once existed.