Ammonite

What’s a nodule?

This ammonite, Asteroceras stellare, lies within a massive Stellare nodule. The rock is known as a septarian nodule, that is a hard, compact mass of sedimentary rock with angular cracks running through it. They are also called concretions. The nodule formed around the ammonite, preserving it from being crushed as more layers of sediment settled. But at a later stage, it shrank causing the radial cracks to form and shattering the ammonite in the process. Later still, calcium-rich waters filled the cracks and calcite crystal grew in them.

Find out more about ammonites on the molluscs pages.

Common name

Ammonite

Scientific name

Asteroceras stellare

Type

Molluscs > Cephalopods


Strata

Lias

Time period

Lower Jurassic

Age

190 million years

Where found

Unknown

Found by

Unknown

Museum

Dorset County Museum, Dorchester

Accession number

DCM.G.14665