Ammonite

Cut and polished ammonite

Several stages of crystallisation preserved this ammonite shell. Pyrite (fool’s gold) crystallised and replaced the shell and chamber walls, then, calcite crystals grew within the centre of each chamber.

The iron pyrites form because, at times, the sea bed became poisonous and stagnant. Without the presence of oxygen, iron and sulphur developed in the sediment and formed iron pyrites. The calcite formed later from calcium-rich water percolating through the rocks. Any cracks or cavities provide the space for the calcium to crystallize as calcium carbonate, or calcite crystal.

Find out more about ammonites on the molluscs pages.

Common name

Ammonite

Type

Molluscs > Cephalopods


Strata

Lias

Time period

Lower Jurassic

Age

195 million years

Where found

Unknown

Found by

Unknown

Museum

Dorset County Museum, Dorchester

Accession number

DCM.G.01251