sedimentary

Ammonite Fossil (Polished Half)

Ammonoidea (subclass)

Hardness: 3.5-4 (Mohs); Color: Brown, tan, and ivory with internal crystalline calcite; Luster: Pearly to Vitreous (when polished); Structure: Logarithmic spiral with internal chambers (septa); Specific Gravity: ~2.7

Hardness: 3
Color: Brown, tan, and ivory with internal crystalline calcite
Luster: Pearly to Vitreous (when polished)

Identified April 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization of extinct marine cephalopods during the Devonian to late Cretaceous periods (approx. 400 to 66 million years ago). The specimen shown has been sliced and polished to reveal calcite-filled chambers.

Uses & applications

Primarily used as decorative display pieces, in jewelry (as pendants), and as educational fossils for teaching palaeontology.

Geological facts

Ammonites are extinct relatives of the modern Nautilus. Their shells are often found turned into pyrite or rainbow-colored ammolite. They are considered index fossils, helping geologists date the rock layer in which they are found.

Field identification & locations

Identify by the planar spiral shape and distinct suture lines between chambers. Commonly found in sedimentary basins worldwide, notably Madagascar, Morocco, and England. For collectors, look for well-defined internal 'crystal' pockets.

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